ProLab Plus Manual The software package for method interlaboratory tests and proficiency tests
Version 2.14
Version: 2.14 For Windows NT, Windows 2000, Windows XP, Windows Vista and Windows 7 December 2011 quo data GmbH Kaitzer Straße 135 D-01187 Dresden Germany phone: +49 351 402 88 67 0 fax: +49 351 402 88 67 19 Email:
[email protected] www.quodata.de Software development Dipl.-Ing. Norbert Schick Omri Teufert Robert Walther Daniel Rothmaler Sebastian Falk Dipl.-Phys. Christian Bläul PD Dr. Steffen Uhlig Manual Dipl.-Math. Sabine Antoni Kirsten Simon Meike Schreitz PD Dr. Steffen Uhlig
The software described in this manual must only be used or copied according to the terms and conditions of the license agreement. Copyright 1998-2011: PD Dr. Steffen Uhlig, Dresden
Contents 1 2
3 4
5 6
Introduction.................................................................................................................. 5 Preparation................................................................................................................... 7 2.1 System requirements ............................................................................................. 7 2.2 Installation.............................................................................................................. 7 2.3 Use of interlaboratory test data of older ProLab Plus versions ............................... 8 2.4 Hotline ................................................................................................................... 8 Overview ...................................................................................................................... 9 General information....................................................................................................12 4.1 Mouse functions ....................................................................................................12 4.2 Database handling ................................................................................................12 4.3 Important buttons ..................................................................................................12 4.4 Overview of buttons in main window .....................................................................13 Selecting ring tests.....................................................................................................14 5.1 Putting ring tests in edit mode ...............................................................................14 File menu.....................................................................................................................16 6.1 Settings in reports, tables and charts ....................................................................16 6.1.1 6.1.2 6.1.3
6.2 6.3 6.4 6.5 6.6 6.6.1 6.6.2 6.6.3
7
General settings ............................................................................................................... 16 Report settings ................................................................................................................. 17 Caption settings ............................................................................................................... 18
Start report ............................................................................................................19 Log info .................................................................................................................19 New database .......................................................................................................20 Change database..................................................................................................20 Backup file ............................................................................................................21 Restore from file............................................................................................................... 21 Store database to file ....................................................................................................... 21 Advice for long-term storage............................................................................................ 21
Database menu ...........................................................................................................22 7.1 Ring test selection.................................................................................................22 7.2 Basic tables ..........................................................................................................22 7.2.1 7.2.2 7.2.3 7.2.4 7.2.5
7.3 7.3.1 7.3.2 7.3.3
7.4 7.4.1 7.4.2
7.5 7.6 7.7
How to work with the tables ............................................................................................. 22 Ring tests ......................................................................................................................... 27 Samples ........................................................................................................................... 28 Measurands ..................................................................................................................... 29 Laboratories ..................................................................................................................... 30
Structure of ring test ..............................................................................................31 Laboratory allocation ....................................................................................................... 32 Sample-measurand allocation ......................................................................................... 33 Sample-measurand-laboratory allocation ........................................................................ 34
Encoding ...............................................................................................................37 Encoding laboratories ...................................................................................................... 37 Encode test portions ........................................................................................................ 38
Participating labs and data yet to be submitted .....................................................40 Characteristics of measurands ..............................................................................41 Test results ...........................................................................................................43
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7.8 7.9 7.10 7.11
Creation of corrected measurands ........................................................................45 Analytical methods and sample preparations ........................................................46 Duplicate ring test .................................................................................................48 Export ...................................................................................................................48
7.11.1 7.11.2 7.11.3 7.11.4
7.12
Test results as CSV file ................................................................................................... 48 Laboratory files ................................................................................................................ 50 Ring test ........................................................................................................................... 54 Email merges ................................................................................................................... 55
Import ...................................................................................................................61
7.12.1 Import of structure with or without test results ................................................................. 61 7.12.2 Addresses, Measurands & samples, Analytical methods/Sample preparations ............. 64 7.12.3 Ring test ........................................................................................................................... 64
8
Test on homogeneity and stability ............................................................................65 8.1 Import test results .................................................................................................65 8.2 Encoding test portions...........................................................................................66 8.2.1 Uniform encoding of all test portions (for laboratories and for homogeneity analysis) and random selection of homogeneity test portions ............................................................................ 66 8.2.2 Random selection of test portions for homogeneity test without encoding test portions for laboratories ................................................................................................................................... 69 8.2.3 Another example for encoding test portions .................................................................... 70
8.3 8.4
Test results ...........................................................................................................71 Computation .........................................................................................................72
8.4.1 8.4.2 8.4.3
Assignment of test portions ............................................................................................. 72 Homogeneity .................................................................................................................... 72 Stability ............................................................................................................................ 76
9
Data selection .............................................................................................................79 9.1 Overview ...............................................................................................................79 9.2 Sample-measurand selection ................................................................................79 9.3 Sample-measurand-laboratory selection ...............................................................81 9.4 Save and load selection ........................................................................................83 10 Statistics .....................................................................................................................84 10.1 Overview ...............................................................................................................84 10.2 Ring test parameters .............................................................................................84 10.2.1 10.2.2 10.2.3 10.2.4
10.3
Option for DIN 38402 A 45: logarithmic calculation ......................................................... 87 Determine assigned value ............................................................................................... 88 Determine target s.d. ....................................................................................................... 90 Variance function ............................................................................................................. 91
Computation of Z-scores .......................................................................................92
10.3.1 Computation tab .............................................................................................................. 92 10.3.2 Score values tab .............................................................................................................. 95 10.3.3 Results tab ....................................................................................................................... 96
11 Charts and tables........................................................................................................98 11.1 Summary results ...................................................................................................99 11.1.1 Right side bar ................................................................................................................. 101 11.1.2 Menu Format.................................................................................................................. 102 11.1.3 Menu Output .................................................................................................................. 102
11.2 11.3
Survey of scores .................................................................................................104 Combination scores ............................................................................................106
11.3.1 Chart of RLP and RSZ ................................................................................................... 106 11.3.2 Laboratory assessment based on RLP ......................................................................... 112 quo data GmbH
11.3.3 Distribution of Z scores .................................................................................................. 118 11.3.4 Control chart and extended evaluation .......................................................................... 123
11.4
Test on equivalence ............................................................................................123
11.4.1 11.4.2 11.4.3 11.4.4 11.4.5 11.4.6 11.4.7 11.4.8
Introduction .................................................................................................................... 123 Define classes of methods ............................................................................................. 124 Recovery equivalence ................................................................................................... 126 Reproducibility equivalence ........................................................................................... 127 Repeatability equivalence .............................................................................................. 128 Sample specific method effects ..................................................................................... 128 Survey of methods ......................................................................................................... 129 Export of results ............................................................................................................. 129
11.5 Tolerance limits and rel. standard deviations ......................................................129 11.6 Youden plot.........................................................................................................130 11.7 Histogram and normal plot ..................................................................................133 11.8 Chart of lab means and repeatability standard deviation .....................................136 11.9 Kernel density estimator (KDE) ...........................................................................138 11.10 HORRAT trend....................................................................................................141 11.11 Principal Component Analysis (PCA) ..................................................................143 11.12 Mandel’s h & k statistics ......................................................................................145 11.13 Laboratory mean values......................................................................................148 11.14 Further reports ....................................................................................................149 12 Quick start: The steps of statistical analysis ..........................................................151 13 Some aspects of the statistical methods in ProLab Plus ......................................156 13.1 When can the method of the Swiss food manual be applied? .............................156 13.2 When can Q/median, Q/Huber or DIN 38402 A45 be applied?............................156 13.3 When can ISO 5725 and DIN 38402 A42 be applied? ........................................156 13.4 When can the Horwitz function be applied? ........................................................156 13.5 When can the empirical Horwitz function be applied? .........................................157 13.6 When can the nested design analysis according to ISO 5725-3 and ISO 5725-5 be applied? ..........................................................................................................................157 14 References ................................................................................................................158
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ProLab Plus – Manual Introduction
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1 Introduction ProLab Plus is a software package specially conceived to facilitate a professional and efficient performance of the various tasks which arise in the context of interlaboratory tests, from statistical analysis to professional data handling. ProLab Plus can be used for the certification of reference materials, the evaluation of analytical methods and for the assessment of laboratories. ProLab Plus will prove useful at every step of a proficiency test. It provides tools which will assist you right from the planning stage, to the realization of homogeneity tests, the automatic data input from laboratories, the application of statistical analysis and the generation of reports. Several statistical methods are available: -
-
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ISO 5725-2 DIN 38402 A42 (German standard for method ring tests for water analyses) Swiss Food Manual Q-Method/Median (Robust statistical method) Q-Method/Huber (Robust method for proficiency tests used e.g. by the German co-operation for water analyses ‘LAWA’)
-
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DIN 38402 A45 (Robust Q-method and Hampel estimator) ISO 5725-5 (algorithm A+S) Nested Design 2x2 (ISO 5725-3/5) Nested Design (ISO 5725-3) (Empirical) Horwitz function ISO 13528
As for the assessment of laboratories, there are also several available protocols, such as the international Harmonized Protocol of IUPAC, ISO and AOAC1, ISO 13528, DIN 38402 A45, CD ISO 20612 and the LAWA2 protocol. More specifically, the laboratories can be assessed by -
Z scores, Zu scores, Zeta scores, Z’ scores Youden plots RSZ (Rescaled Sum of Z Scores) RLP (Relative Laboratory Performance) Percentage of successful measurements
ProLab Plus allows flexible data input, whether manual or through the import of digital files. The simple data entry program RingDat is provided which may be forwarded to the participating laboratories without extra charge. Additional information on the laboratories and the methods can be entered into the system, such as addresses, the determination limit and the detection limit, the sample preparation method and the analytical method. 1
Michael Thompson and Roger Wood (1993), International Harmonized Protocol for Proficiency Testing of (Chemical) Analytical Laboratories. Journal of AOAC International 1993, Vol. 76, 926-940. 2 AQS der Länderarbeitsgemeinschaft Wasser für Wasser-, Abwasser- und Schlammuntersuchungen (Working Group on water issues of the federal states and the federal government)
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ProLab Plus – Manual Introduction
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A powerful data selection program assists the user in the evaluation and the presentation of results, enabling him to sift data as convenient, to generate individual reports or reports for selections of laboratories, and to set up and save selection patterns. Up to four selection patterns per ring test can be saved. All results are stored in the database. Comments can be saved for participants, measurements and within charts. Numerous specialised chart-generating functions are provided to assist in the presentation of results, while a powerful report designer enables the generation of editable reports. Reports can be exported into the formats PDF, RTF (Word), XLS (Excel), HTML, Text and CSV. Charts can be converted into Bitmaps (BMP), Scalable Vector Graphics (SVG) and the Windows Meta File format (WMF).
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ProLab Plus – Manual Preparation
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2 Preparation 2.1
System requirements
The hardware and software requirements for ProLab Plus are listed in the following table. Processor RAM Hard disk Operating System
Intel Pentium or compatible with at least 1 GHz (> 2.4 GHz recommended) 512 MB > 300 MB free Windows NT (with service-pack 5), Windows 2000, XP Professional (not Windows XP Home Edition), Windows Vista and Windows 7.
ProLab Plus runs stable under Windows 7, and all calculations and reports work as expected.
2.2
Installation
1. If you have an existing ProLab Plus version, please backup your current ProLab Plus program directory and your database before installing the new version into the current program directory. The path to the database is shown at the very top of the ProLab Plus window. 2. If you downloaded a setup program from our website, please run it now. If you want to install ProLab using a CD, please put the CD into the drive. The setup program will start automatically. If not, please run setup.exe in the root directory of the CD. 3. Follow the installation dialogue and use the directories proposed. Upon successful installation, a program group ProLab will be created, which contains ProLab, a help file for the Report Designer (Qrduser) and a program for direct input of data from laboratories (RingDat). 4. Run ProLab Plus. 5. After the first start you will see a registration dialogue with a registration number. You can phone quo data GmbH (+49 351 402 88 67 0) or send an email (
[email protected]) and you will get the necessary key. After input of the key press “Save”. Alternatively, you can proceed as follows. Close the program ProLab Plus. In the program directory you will find the file REGISTER.INI. Send this file via email to
[email protected]. Within one working day, you will receive a new file REGISTER.INI with the key. This file must be copied into the program directory of ProLab, replacing the original file.
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2.3
.
ProLab Plus - Manual Preparation
Use of interlaboratory test data of older ProLab Plus versions
Since ProLab 2003, a new database format is used (ADS, developed by Sybase which belongs to SAP). The current version ProLab Plus 2.14 uses ADS 10. It is therefore not possible to directly access older BDE databases. However, the conversion program „ProLabMigrator.exe" allows simple conversion of the old databases. Start this program, select the directories for the BDE database and the ADS database and start the transfer.
2.4
Hotline
In case of problems use the hotline of quo data: +49 351 402 88 67 0 or send an email to:
[email protected].
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ProLab Plus – Manual Overview
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3 Overview The main menu is the starting point of every evaluation using ProLab Plus. You are in the menu as soon as you successfully start ProLab Plus. The main menu contains eight modules, which can be selected using the common Windows techniques (mouse, arrow keys or input of the corresponding character): -
File Database Homogeneity / Stability Selection Statistics Charts and tables Window Help
The modules are ordered in such a way that, in the performance and evaluation of a ring test, they are typically activated from left to right. One starts in the module File with the definition of settings for reports and data base tables. That is followed by the description of the ring test, of the samples and measurands that are to be examined and evaluated, and of the encoding of laboratories and samples. Once the results start coming in, they will thus be able to be imported or manually entered. All necessary functions for the latter procedure are located in the module Database. If required, a test of the homogeneity of the samples in preparation for the ring test can be conducted in the module Homogeneity / Stability, which also provides the necessary functions for any stability tests to be conducted later on. The Selection module provides all relevant tools for the selection of samples, measurands and laboratories to be included in assessment and analysis procedures or in the presentation of results. The evaluation, analysis and assessment procedures are then carried out in the module Statistics, while reports and charts in various layouts can be generated and displayed in the module Charts and tables. Each step within this sequence affects subsequent steps. All statistical results obtained at any stage will be directly stored in the database. Earlier results of the same ring test will be overwritten automatically. If there are some modifications to implement ( e.g. in the calculation of Z scores) it is not necessary to create a new test: changing the data at the earliest relevant step is sufficient. An overview of important functions in ProLab Plus is given in the following table.
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ProLab Plus – Manual Overview
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File
Settings Formats, general report settings and report designer Generate database, change database, backup files
Database
Database and data input Ring test selection Basic tables: ring tests, samples, measurands (analytes), laboratories Structure of ring test: assignment of laboratories and measurands Encoding: Encoding of laboratories and samples Participating labs and outstanding data Characteristics of measurands: reference values, units, conversion factors et al. Definition of analytical methods and sample preparations Test results Creation of corrected measurands Duplicate ring test Export: CSV files, laboratory files, ring test, email merge Import: structure/test results, addresses, measurands & samples, analytical methods & preparations and ring tests
Homogeneity / Stability
Import and analysis of homogeneity and stability test results Import test results Test portion encoding Test results Computation of homogeneity and stability
Selection
Selection of data for statistical analysis and the presentation of results Selection of samples and measurands Selection of samples, measurands and laboratories Save and load selections
Statistics
Analysis and assessment Calculation of statistical parameters of the ring test (lab means, lab s.d., overall mean, reproducibility s.d. and repeatability s.d., specification of target value and target s.d.) Calculation of tolerance limits and single scores (Z scores, Z u scores, Zeta scores, Z’ scores)
Charts and
Charts and tables of the statistical analysis
Tables
Comprehensive presentation of results for each sample-measurand combination separately Survey of scores Combination scores and ring test-spanning analyses Test on equivalence Tolerance limits and rel. standard deviations
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ProLab Plus – Manual Overview
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Youden plot Histogram and normal plot Chart of repeatability standard deviations Kernel density estimator (KDE) HORRAT trend Principal component analysis Mandel’s h & k statistics Laboratory mean values per sample and per measurand Further reports: number of test results and labs, survey of test results, method characteristics, summary of outliers, individual reports Help
Help function Program update: check for new version
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ProLab Plus – Manual General hints
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4 General information 4.1
Mouse functions
The main functions of the program can be activated by using the left mouse button. Some additional functions ( e.g. number of columns and column-width in tables) can be activated by using the right mouse button.
4.2
Database handling
In some forms, data sets ( e.g. measurands, ring tests, labs, samples, test results) can be accessed, edited, added or deleted. The following commands are available for this purpose: Back
Go to the previous record
Forward
Go to the next record
Insert
Insert new record
Delete
Delete selected record
Save
Save changes
Cancel
Cancel editing
Please note that it is not possible to undo changes in the database. Therefore it is very important to make a backup of the database at the beginning of each session, so the original database can be recovered. For the creation of the backup select File – Backup file.
4.3
Important buttons
The following list explains some important buttons frequently used in the program: Close Closes current window. Report
Click this button to display a report preview for the selected data. In many cases, it is also possible, by simultaneously holding down the SHIFT key , to open a spreadsheet which allows data editing and storage in a way similar to the Excel program.
Help
Activates help for the current window.
Save
Click this button to save tables or charts as a file.
Print
Click this button to print out reports or charts.
Lab code
Click this button to turn switch between the laboratory name (LName) and the laboratory code (LCode) in charts and tables.
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ProLab Plus – Manual General hints
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Overview of buttons in main window
The buttons in the main-menu toolbar make it possible to easily activate the most important and commonly used functions. The following table offers an overview of these shortcuts. Change ring test and define working mode Settings Survey of test results Edit data of basic tables Assignment of participating laboratories Assignment of measurands to samples Assignment of measurand-sample combinations to laboratories Encoding laboratories Encoding test portions Ring test-specific characteristics of measurands Edit test results Select sample / measurand for further use Select sample / measurand / laboratory for further use Save selection Load previously saved selection Calculation of ring test parameters Calculation of scores and laboratory evaluation Chart/table of laboratory mean values and standard deviations Survey of scores Chart of tolerance limits and rel. standard deviations Youden plot Histogram und normal plot Table of laboratory mean values and scores – per measurand Table of laboratory mean values and scores – per sample Help
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ProLab Plus – Manual Selecting ring tests
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5 Selecting ring tests Many features of ProLab Plus are specific to the selected ring test. Subsequently used modules and functions always refer to the ring test previously selected in the selection box.
Figure 1: Main menu
There are two different working modes for a ring test. They can be selected from the main menu via the button Ring test or via the menu Database – Ring test selection.
5.1
Putting ring tests in edit mode
If you want to work on a ring test, e.g. enter test results, carry out calculations etc., select the checkbox in the Access column for the relevant ring test and double click on the ring test, or close the window and select it from the selection box on the top of the main window.
Figure 2: Database – Ring test selection
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ProLab Plus – Manual Selecting ring tests
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If you only want to view the results and prepare presentations, do not select the check box, but double click on the relevant ring test or select it from the selection box on the top of the main window. No data input or changes are possible in this mode. If all ring tests should be included in a presentation, all of them need to be made accessible. Therefore click on the button Make all ring tests accessible. If you don’t want any of the ring tests in the edit mode, click on Make all ring tests read-only. If a ring test is marked in red, it is currently opened on a different computer. You can also open it and make changes, but this may lead to inconsistencies in the database.
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ProLab Plus – Manual File Menu 16
6 File menu The File menu contains settings for reports and tables, the report designer and selection of the database.
6.1
Settings in reports, tables and charts
The Settings dialogue box allows you to choose different settings for how information will be displayed in the reports, tables and charts. This includes the specification of number formats and the name of the institution. Furthermore, the currently used logo is shown. It may be changed via the button Change. Changes will be saved automatically upon closing the window or switching between tabs. 6.1.1 General settings This tab enables you to enter general settings such as institution name, number format, creation date, chart size and colours. If the check boxes for number format, date or default chart size are marked, these settings will apply to all tables, forms and graphics displayed.
Figure 3: File – Settings – General
The characters for formatting numerical values are:
.
Decimal separator
0
this digit must be a numeric character
#
this digit may be a numerical character
E+
exponential notation
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ProLab Plus – Manual File Menu
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By clicking on Reset chart settings all saved chart settings and profiles as well as information regarding size and colour are reset to the default setting. By clicking on Reset non-chart settings and confirming the list of configuration files to be deleted, all information regarding institution, date and number format and many other settings stored by other ProLab windows are reset to the default setting. By marking the checkbox Highlight outliers of type E in the summary results this option can be selected. For further explanation of outliers of type E please refer to chapters 10.2 and 11.1. 6.1.2 Report settings The tab Reports contains a comprehensive list of commonly used report templates. ProLab Plus offers a wide variety of templates, so the time-consuming task of designing reports can thereby often be avoided.
Figure 4: File – Settings – Reports
Select a report and click this button to open the Report designer module. Alternatively, a double click on the report will open the same module. Any changes become ef-
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ProLab Plus – Manual File Menu
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fective upon saving the report in the Report Designer module. Customised report are highlighted in bold writing. Since for some reports the data is missing in the templates, the report might look somewhat strange at first when using the preview. Upon input of data, however, you will find that the report looks fine. Using this button will reproduce the original report template as created by the installation program. This button is only relevant for reports highlighted in bold writing, that is to say, for customised report templates. Designing new reports is possible, either directly or by using the Report Designer module. This button opens the Report Designer for creating a new report. This button allows you to edit existing reports. User-defined reports can be accessed via the menu Charts and tables – Further reports – Own reports. The last column in the table shows the date of the last adjustment of the report template, not the date of the last time the report was used. 6.1.3 Caption settings The Captions tab contains standard abbreviations for a number of names for titles and headers in charts and tables (e.g. column headers) and enables you to customise them. Please be aware that these settings will not become effective in every report. In some cases, the particular report has to be adjusted using the Report Designer.
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ProLab Plus – Manual File Menu
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Figure 5: File – Settings – Captions
6.2
Start report
By choosing the menu item File – Start report or pressing F8, you can determine the page number on which the next report you want to print will start. This is helpful when there are several reports to be compiled, i. e. you want to combine them into one report with successive page numbers.
6.3
Log info
During a ProLab Plus session the following information is saved: Time of log in and log out User name Imported data Test results that have been changed Protocol of calculation of ring test parameters Protocol of calculation of scores.
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ProLab Plus – Manual File Menu
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To access this information please choose Log info from the File menu. To open the report preview containing the information from all ProLab Plus sessions use the Report button.
Figure 6: File – Log info
6.4
New database
Via File – New database a new and empty database can be generated automatically in a new directory. This might be appropriate when different ring tests should be saved in different databases. Generally, saving ring tests in one and the same database might be reasonable, e.g. for an analysis spanning several ring tests; however, too many ring tests in the same database may slow down the program noticeably. After selecting a directory from the list or entering a name for a new directory in the edit window, the structures of the tables in the current database are copied to the target directory. WARNING: Existing tables in the target directory will be overwritten whereby any data contained in these tables will be lost.
6.5
Change database
It is possible to change database directories, that is to say, to transfer a database with all the data relative to a ring test from one directory to another. Make sure that the new database directory contains all required tables, otherwise your work may be compromised. This is best achieved by using the Backup file command or by copying the database directory outside of
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ProLab Plus – Manual File Menu
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ProLab Plus.
6.6
Backup file
This command allows backing up the entire database (all tables) in a compressed file and recovering it again from this file if necessary. LHARC is used as compression format. For saving your data, select a target folder and enter a file name. When quitting ProLab Plus you will be asked whether you want to create a backup copy of your database. Additionally, you can manually backup the database to a folder of your choosing by using the following tab.
Figure 7: File – Backup file (Backup of database „Demo“)
6.6.1 Restore from file In this window, all backup files that have been created so far (and still exist) are listed. In order to restore one of them, simply select it from the list and click the button Restore from file. Alternatively you can choose Select file… in the first row of the table and specify the LZH file you want to restore. WARNING: Any existing data will be overwritten and thereby lost. If you want to restore a database without overwriting existing data and tables, please create a new database as described in section 6.4 before restoring. 6.6.2 Store database to file In order to create a backup of your database, you have to select a target file first. Normally that will be a new file, which can be created via the first row Select file… Alternatively an existing file from the list can be chosen. To start the process simply click Store database to file. Please note that any existing data will be overwritten and thereby lost. 6.6.3 Advice for long-term storage Although there are several programs of other developers or Open Source communities which can open LZH files and/or the contained Advantage Database System files, this binary format may not be the best choice for long-term storage of ring test data. It is recommended instead to export plain-text CSV files additionally (please refer to chapter 7.11.1).
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ProLab Plus – Manual Menu Database
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7 Database menu 7.1
Ring test selection
Please refer to chapter 5.1, Putting ring tests in edit mode.
7.2
Basic tables
A ring test is defined by the samples, the measurands and the laboratories. Therefore, the tables for the ring tests, samples, measurands and laboratories constitute the foundation of the database. The basic tables can be reached via Database – Basic tables. In these tables, all the information on samples, measurands and laboratories is entered, but no allocation ( e.g. e.g. which measurand is analysed by which laboratory on which sample) is carried out yet. 7.2.1 How to work with the tables The data tables offer a powerful tool for working with the database. The data can be sorted and grouped in several ways, fields can be added and removed and whole tables or selections can be saved in different formats. In the following, several possibilities for working with the tables are described. However, it must be noted that not all commands are available in all tables. The most important buttons are Save
Save changes
Cancel
Cancel editing
Add
Add new data
Delete
Delete selected data
New data ( e.g. ring tests or samples) can also be added by clicking into the first row of the respective table. Please note that the names of the ring tests, the measurands, the samples and the laboratories are unique identification labels. Therefore they should not be changed later on. Name must only contain capital letters and numeric characters. Description can be filled and/or changed later. If the Description field is left empty, Name will be entered automatically. When clicking with the right mouse button onto the column headers, a pop-up menu opens within which the available commands are in dark letters (see Figure 8). These commands will be explained in more detail in the following:
Reset table settings All changes in the appearance of the table can be undone by choosing Reset table settings from the pop-up menu. You get there by a right click with the mouse onto any column header.
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ProLab Plus – Manual Menu Database
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Sorting The tables can be sorted in ascending or descending order (with respect to a selected column) either by left-clicking in the respective column header or by selecting the commands from the following pop-up menu, which opens by rightclicking into a column header.
Figure 8: Pop-up menu after right mouse button click into column header
Add and remove columns, adjust order The order of the columns can be changed by drag & drop: simply click in a column header and by keeping the mouse button pressed move the column to the desired position. Unnecessary columns may be hidden by deselecting the respective column from the list that can be reached via the button Visible columns. A column may also be removed by clicking in the header and selecting Remove This Column from the pop-up menu. If formerly removed columns or further columns should be added to the table, simply select the column from the list under Visible columns or select the Field Chooser from the pop-up menu. From the field chooser, a column can be moved to the table by drag and drop. In order to add or remove several columns at once, right-click anywhere inside the table (not in the headers) and select Select columns from the pop-up menu while keeping the Shift key pressed. The column width can be adapted manually by moving the separators of a column. The best fit, i. e. the column width that enables to see the whole content of the column without wasting too much space, can be obtained by double clicking on a separator or by choosing Best Fit from the pop-up menu. An optimal width of all columns can be obtained via the command Best Fit (all columns) from the pop-up menu. Grouping A table can be grouped with respect to column entries and will thereby be divided into subtables. Grouping can be done by marking the desired column and selecting Group By This
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Field from the pop-up menu. After selecting this command, a dark grey box will appear above the table indicating the column according to which the grouping is carried out. A further possibility for grouping is to select the command Group By Box from the pop-up menu. The dark grey box then appears without any column header name. Now the column according to which the grouping should be carried out can be moved to the dark grey box via drag and drop. In , the table grouping of measurands with regard to the column Category 2 is shown. As there are three entries in the Category 2 column, the grouped table now consists of three sub-tables, one for light metals, one for heavy metals and one for gasses. These sub-tables can be opened or closed via the + / - buttons. Of course, a table can be grouped several times in succession. Thereby more and more subtables are generated. This grouping can be done again either by successively marking column headers and selecting the command Group By This Field from the pop-up menu or by selecting the command Group By Box once and then successively dragging fields to the grey box above the table. In both cases, the hierarchy of the grouping will be shown in the dark grey box.
Figure 9: Basic table of measurands grouped by Category 2
Column width Using the menu option Best Fit, the width of the columns will be adjusted according to the content. To adjust all columns at once the shortcut Ctrl + Addition (on the numerical keyboard) can be used.
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Copy Whole tables or selection thereof can be copied to the clipboard and, e.g., inserted into an Excel table. For this purpose use the right mouse button within the table (not in the headers). Then a pop-up menu will be displayed where you can select Copy table or Copy selection. With the first command, the whole table is copied. With the second command, only the row in which has been clicked is copied, along with the column header.
Figure 10: Pop-up menu after right mouse button click into table
Save All tables can be saved in different formats: text file, Excel file, XML file or HTML file. The table can be saved as a PDF or RTF file from within the report preview. For this purpose use the right mouse button within the table (not in the headers). Then a pop-up menu will be displayed where you can select the desired saving format. The information of a grouped table is always completely saved independently of the way it has been displayed in ProLab Plus, i. e. the information of sub-tables closed in ProLab Plus will be saved as well. Of course, the grouping is saved, too.
Search text After clicking this menu item, a search bar will be shown. That bar can be opened by using the shortcut Ctrl + F alternatively. To close the bar, click on the cross on the left side or use the Esc key. Select columns This option opens a list with all columns that can be shown. There are three different types of lists: 1. In most windows, the default setting leads to a list with check boxes, which makes possible a swift selection of columns to show or hide. 2. If you decide to change the visibility of more than one column at once, hold the Shift key down while clicking on the menu option ‘Select columns’.. A window appears in which you can show or hide all columns by using the keys ‘>>’ or ‘ 2, yellow otherwise.
RRLP
The laboratory’s rolling RLP average, calculated as the mean of the best 4 RLPs taken from the current and its 4 preceding ring tests. Please be aware that no RRLP can be calculated for the first three active (i. e. Edit-mode) ring tests. Thus, in order to display an RRLP for a ring test, the four ring tests before the current one need to be made accessible (Edit mode) and the ring test parameters have to be calculated for those ring tests as well.
P value
A P value below 0.05 is considered an indication for a systematic bias in the test results.
By clicking on a column header the data is sorted with respect to the corresponding criterion. A double-click on any laboratory’s row will open the report for that laboratory and the currently selected measurand. Right-clicking on the table allows copying to the clipboard for re-use in applications such as Microsoft Excel.
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Figure 78: Results per analyte
On the bottom of the window, the performance plot for the current laboratory and measurand is shown. This chart plots a maximum of three curves: 1. the RLPs for all active (i. e. Edit-mode) rounds 2. the RRLPs for all active ring tests and 3. the median of the RLPs of all laboratories Again be aware that no RRLPs can be calculated for the first three active ring tests. The following options are available on the left of the chart: Hide rounds without RRLP
This option will hide all ring tests for which a RRLP is available for no laboratory.
Show future rounds
This option is only available if the current ring test is not the last.
Show date below round
Displays the Date of analysis as defined in the Basic tables below each ring test on the X-axis. Please note that in order for that option to be meaningful, a date needs to be entered for each ring test. As the date text needs more space
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than the ring test number, some ring test labels might disappear but the data points will remain in the chart. Number format
Change the format of the date used. The default is yyyy"/"mmm. The following codes can be freely combined: Code Meaning yy yyyy "/" m mm
two-digit year four-digit year single slash month as number same as m, but with leading zero for single-digit months mmm abbreviated month mmmm full month name ddddd full date, e.g. 29/05/2010 The last three settings depend on the configuration of Microsoft Windows within the control panel. The chart options will also be used in the report. With a right-click, more functions for the chart are offered. Double-clicking the chart will open an extended chart editor.
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Results per lab & kernel density estimation
Figure 79: Results per lab
The second tab contains, from top to bottom: a selection box for the laboratory of interest. In this box, all laboratories that took part in the current ring test are shown. They are sorted according to their unique laboratory name (as entered under Database – Basic tables). a table of measurands, the last four columns containing the same information as the corresponding columns of the table in the first tab a chart with the kernel density estimation (KDE) of the distribution of the standardised test results (measured values divided by assigned value) of all laboratories is shown for the selected measurand. For each sample, separate kernel densities are shown in different colours. The kernel density over all four test samples is displayed as a thick black curve. The individual standardized results of all laboratories are shown as circles. The colour of the circle coincides with the colour of the curves. The circles can be displayed on the overall curve or on the individual curves, depending on which of the options on the left has been selected. Furthermore, by checking the option Current laboratory only, it is possible to display the standardized results only for the currently selected laboratory rather than for all laboratories. quo data GmbH
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These settings are then applied in the report as well. With a right-click in the chart, further options can be selected. Double-clicking the chart will open an advanced chart editor. Summary of results On the last tab, the results submitted by the laboratories, the assigned value and the standardised results (ratio of result and assigned value) are shown for each laboratory, each measurand and each sample of the current ring test (see Figure 80).
Figure 80 – Standardised values tab with popup menu. A filter button is highlighted with a red circle
At the top of the window, limits for the standardized values can be specified. Values below the lower limit and above the upper limit are highlighted in red . The limits are not used for any calculation, but only serve as a display option. Check the box on the left of the range to display only standardised results lying outside the limits (i. e. the ones that are marked in red already). The table may be grouped by measurand and laboratory by checking the relevant box above the table. Once the table has been grouped, a collapsible bar is displayed above each group. This bar also contains the average standardised value within the group. If the table is not
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grouped, the list can easily be sorted by clicking on the text of any column header. A small triangle will indicate the sorting direction. In some cases, the current selection does not contain all laboratories that took part in the current ring test. If the selection should be taken into account in this table, please check the relevant box above the table. It is also possible to filter the data within the table. For example, click on the small arrow button highlighted in Figure 80 to restrict the view to just one laboratory. To remove the filter, click the [x] button at the bottom left of the table. Filters can also be combined. A click with the right mouse button on the table opens a menu that allows copying it to the clipboard or saving it in various file formats. A right-click on any column header opens a different menu to customize the way data is displayed. Reports The certificate-like report contains the results of one laboratory for one measurand on one page. This report can be displayed either for the currently selected combination of laboratory and measurand (This report is also generated by double-clicking on a table row within the Results per Measurand and Results per lab tabs) or for all measurands which the currently selected laboratory has analysed (separate page for each measurand) or for all laboratories that analysed the currently selected measurand (separate page for each laboratory) or for all combinations of laboratory and measurand available in the current ring test 11.3.3 Distribution of Z scores The Distribution of Z scores window displays a histogram and a scatter plot for selected ring test-sample-measurand combinations over all samples. The difference with the Histogram and normal plot chart (section 11.7) is that here you can select more than only one ring test, measurand and/or laboratory. First you have to select the ring tests, measurands and laboratories you want to include in the histogram. This can be done on the Selection tab. The selection is carried out by marking the corresponding ring tests, samples and laboratories. It is also possible to select or deselect all ring tests, measurands and laboratories. If categories for measurands or laboratories have been defined, all measurands or laboratories within one category can be selected or deselected with the buttons “+” or “-“.
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Figure 81: Charts & tables – Distribution of Z Scores – Selection
On the Histogram/KDE tab you can see the histogram of the Z scores corresponding to your selection. The Z scores can be displayed by laboratory, by measurand, by laboratory and measurand or for all data previously selected. In the upper part of the window you can determine whether the kernel density estimation (blue) of the Z score distribution and the standard normal distribution (green) should be displayed as additional information. Furthermore, extreme Z scores smaller than -6 and greater than +6 can be excluded from the chart. The x-axis represents the Z scores obtained, while, for the laboratory-wise and laboratoryand-measurand-wise chart options the y-axis represents the relative frequency with which the selected laboratory obtained the respective Z score; for the remaining two chart options the y-axis represents the relative number of laboratories that obtained the respective Z score.
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The performance of a laboratory can be assessed according to the percentages given in the top right corner of the chart. These percentages indicate the relative number of scores between -1 and +1, between -2 and +2, between -3 and +3 and finally between -6 and +6. In brackets the theoretical values according to the normal distribution are shown. In the following chart the distribution of the Z scores of a laboratory with a good performance is shown. Only about 3 % of the 38 scores lie outside the tolerance limits of -/+ 2. In fact, these 3 % coincide with one score which is above +3. The remaining 97 % of the scores lie between about -2 and +2.
Figure 82: Charts & tables – Distribution of Z scores – Histogram/KDE
In the window Scatter different scatter plots on the basis of the Z scores selected on the Selection tab are available. It is possible to choose between displaying Z scores, cumulated Z scores and relative deviations (in %) of the laboratory mean value from the assigned value. Furthermore, it is necessary to determine whether laboratories, measurands, ring tests or samples should be shown on the horizontal axis. It is then possible to specify whether the values are shown per lab, per measurand, per lab and per measurand or for all data previ-
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ously selected. The options per lab and per measurand are only available if either the ring tests or the samples are shown on the horizontal axis. In following figure displays the Z scores of the same laboratory as in Figure 82. According to this chart, copper in sample 51 can be identified as the source of the Z score above +3.
Figure 83: Charts & tables – Distribution of Z scores – Scatter
In the following Figure 84 several display options of the scatter plot are shown. These are based on the data of two ring tests with 2 samples each, analysed for 4 measurands by 20 laboratories. Except for the values of laboratory 01, all laboratories submitted consistent data. In the chart Z scores for mercury per lab it can clearly be seen that the Z scores of the laboratories of both ring tests for the same samples are very similar: the red and the blue curve as well as the green and the orange curve almost lie on each other. Only for laboratory 01 the Z scores differ considerably. This is also pointed out in the next chart “Z scores for lab 01 per measurand”, especially for mercury (HG) large discrepancies can be observed: while the Z score for sample 01 in the first ring test R3 (blue) lies within the tolerance limits a high Z scores clearly above the upper tolerance limit can be seen for the same sample in the second ring test R4 (red). Similar trends can be observed for measurands nickel (Ni) and zinc (Zn). The deterioration of the results of this laboratory from one ring test to the next can also be seen quite well in the next chart Z scores for lab 01 per ring test:, the Z score for mercury (green) clearly increases from -1.5 in ring test R3 to +3 in ring test R4. Whereas the chart Z scores for mercury per ring test shows that only laboratory 01 exhibits such remarkable deviations for the measurand mercury, while the curves for the remaining laboratories are rather horizontal, i. e. for these laboratories hardly any differences between the Z scores for mercury of both ring tests can be detected. By displaying the Z scores per sample once for labora-
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tory 01 over all measurands and once for mercury over all laboratories, the strong deviations of the Z scores of laboratory 01 become clearly visible once again.
Figure 84: Charts and tables – Distribution of Z scores – Scatter
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11.3.4 Control chart and extended evaluation In this window, the control chart is generated and the combination scores per measurand and for all measurands are calculated. The calculation is based on the parameters assigned value and target s.d. as defined under Statistics – Ring test parameters. There is the possibility to cap Z scores, i. e. a capping limit is defined. According to the protocols of AOAC, IUPAC and ISO, a capping limit of 3 is recommended. This means that instead of scores such as -3.3 or -8.9, the score -3 is assigned. Capping is only useful if combination scores are about to be calculated. If there were no capping, a single gross outlier could distort all combination scores. After specification of the single scores, the parameters for confidence intervals as well as the assigned variability limits have to be defined. The laboratory, environmental or consumer risk ( e.g. 0.1) describes the acceptable statistical error probability of a laboratory being wrongly evaluated, whereas the variability limit ( e.g. 0.2) describes a hypothetical maximum relative error. Please note that the calculation of Lischer scores takes a certain amount of time. Accordingly, the calculation of these scores can be activated separately. On the tab Control chart you can find a graphic display of combination scores for all measurands. These can be shown either lab-wise or for all laboratories.
11.4 Test on equivalence 11.4.1 Introduction The principle of equivalence states that two analytical methods have to be considered as equivalent if their deviation falls below a certain value to a certain level of statistical significance. The proof of equivalence always comprises several aspects. Thus in the context of a ring test it has to be ensured that besides the deviation of the general mean (recovery equivalence), the standard deviation under repeatability (repeatability equivalence) and reproducibility (reproducibility equivalence) conditions do not exceed a given value. The greater the number of replicates of measurements performed, the sharper the conclusions on equivalence can be formulated, from a statistical point of view. If there are only a few replicates, equivalence can only be proved if relatively large deviations are accepted. Equivalence can a priori only be examined for one single sample. However, measurements of different samples can be considered together, as long as it is ascertained that samplespecific method effects are negligible. Otherwise it cannot be excluded that the result does not reflect the efficiency of the analytical method in general, but may be influenced by the particular sample selection. Regarding recovery equivalence, this can be determined by calculating the difference between the sample specific and the average relative deviation. If the confidence interval calculated for the variances of this difference covers the zero point for all samples, it can be concluded that sample-specific method effects are not provable. You can
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find a corresponding chart in the window Charts and tables – Test on equivalence – Sample specific method effects. (see also section 11.4.6) 11.4.2 Define classes of methods Basically every combination of measurand and method should undergo an independent test on equivalence. Here, method denotes the combination of sample preparation and analytical methods. For practical reasons ( e.g. insufficient data) it may be reasonable to combine several methods. Of course this is only permitted if it can be assumed that the methods are equivalent. The calculation of equivalence is then carried out for every combination index, no matter whether it contains only one method or a combination of equivalent methods. At first the classes of methods have to be defined. This can be done in the window Charts and tables – Test on equivalence – Classes of methods. The currently defined classes and the respective colour codes are displayed on the bottom side of the window. To add, edit or delete classes of methods, click on the Edit class of method button.
Figure 85: Test on equivalence – Edit classes of methods
The assignments of the classes to the single methods must then be carried out. To do this, select the relevant class on the bottom. Double clicking on a cell of the method/measurand table allocates the chosen class and colours the cell respectively. A repeated double click deletes the allocation. For these operations you can also use the buttons in the above menu: Add class reference, Delete class reference. You can also select several cells and assign them to one method class together..
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Figure 86: Statistics – Test on equivalence – Classes of methods
You can choose between displaying all measurands available in the database or only the measurands belonging to Category 1 or Category 2. A summary of the available data of the current allocation is shown at the bottom of the Classes of methods table.
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11.4.3 Recovery equivalence Equivalence with respect to recovery means that the relative difference of the overall mean values of the reference method and the method being evaluated falls below a particular tolerance value Recovery . Typical values for Recovery are in the range of 10-20%. For the level of significance usually a value of 5%, 10% or 15% is defined. Click on the button Start to carry out the calculations using the current settings.
Figure 87: Statistics – Test on equivalence – Recovery equivalence
Besides the general statistical parameters for the analyses of the samples by different methods, the parameters of the determination of equivalence are also displayed: Non-centrality parameter of the assumed non-central t-distribution. Critical value that is derived from the non-central t-distribution for the specified parameters and the non-centrality parameter. On the basis of the preceding, the Maximal tolerated empirical deviation can now be computed. If the actual Empirical deviation is smaller than the maximal tolerated empirical deviation, the equivalence for the specified tolerance Recovery is proved at the level of significance
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11.4.4 Reproducibility equivalence Two methods are equivalent with respect to their reproducibility standard deviations, if the latter differ by less than a tolerated factor R . Appropriate values for the maximal tolerated ratio R are around 1.6.
Figure 88: Statistics – Test on equivalence – Reproducibility equivalence
The statistical parameters for the reproducibility standard deviation of both methods are displayed as well as the Standard deviation of the empirical difference, the (1-)-quantile of the standard normal distribution, -
from which the Maximal tolerated empirical difference for the specified R and is
computed. If the actual Empirical difference is smaller than the maximal tolerated empirical difference, the equivalence for the specified ratio R is proved at the level of significance
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11.4.5 Repeatability equivalence The equivalence of two methods concerning the repeatability standard deviation is computed analogously to the reproducibility standard deviation. Accordingly, the values of r should also lie around 1.6. The output is analogous to that of the reproducibility standard deviation.
Figure 89: Statistics – Test on equivalence – Repeatability equivalence
11.4.6 Sample specific method effects As explained in the introduction (see section11.4.1), an evaluation over all samples is only permitted when the methods show no sample-specific effects. In the chart Sample specific method effects, the confidence intervals for the differences of the sample specific to the average relative deviation are shown. If all of them cross the zero line, no significant samplespecific method effects can be detected.
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Figure 90: Statistics – Test on equivalence – Sample specific method effects
11.4.7 Survey of methods A survey of all methods for every measurand is shown on the tab Survey of methods. 11.4.8 Export of results The results shown in the various tables can be exported in several formats. By clicking with the right mouse button in a table, the following context menu can be opened: Copy Copy selection
Copies the whole table to the clipboard. Copies the marked selection of the table to the clipboard. Please note that this can be pasted into an Excel table, but not into a Word document. Save in file Saves the table as a text file. Copy to Excel Saves the whole table as an Excel table. Excel must be available on the PC Set column width Enter a value to set the column width. Adapt column width automatically Adapts the column width automatically. Line break Line break in column header if necessary. Select column Selection of columns to be shown in the table
11.5 Tolerance limits and rel. standard deviations In this window you see two charts that represent the tolerance limits, variances and standard deviations on the basis of the assigned value. Buttons for a quick adjustment of the chart settings are available in the upper part of the window:
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Comment
Allows editing and deleting texts that have been included as comments in the chart.
Report
In submenus different options for the report are offered. A preview of what is to be printed is always shown.
Figure 91: Charts and Tables – Tolerance limits and rel. standard deviations
Further information on the values displayed in the chart can be obtained by moving the mouse pointer close to the value. The pointer takes on the shape of a hand. If you now press the left mouse button, a window with the corresponding laboratory name, assigned value and relative standard deviation opens up.
11.6 Youden plot The Youden plot window displays a combined graphic of the results of two samplemeasurand combinations. Such a presentation allows identifying systematic effects in the laboratory-specific deviations. The following combinations are possible for the two axes:
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per measurand: the two axes represent two different samples for the selected measurand across measurands: all measurands of the two samples are combined per sample: the two axes represent two different measurands for the selected sample across samples: all samples with the two measurands are combined
Depending on the combination you have to choose the common measurand or sample and the desired measurands and samples for the axes via the scroll-down menus on the right. For the combinations over all measurands and over all samples the scroll-down menu for common measurands and common samples are not displayed.
Figure 92: Charts and tables – Youden plot – Zu scores (per measurand)
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Figure 93: Charts and tables – Youden plot – Laboratory mean values (per sample)
The graphic can be printed or edited by using the following buttons: Code
Toggles between laboratory name and code
Report
Opens a window with a report preview in the currently selected report format
Frame
Toggles between no frame or a frame as square, ellipse or circle. The ellipse is drawn for a significance level of 5 %.
Limits
Change of the value of the borderline. The value equals the radius of the circle or half the edge length of the square.
A graphical combination per sample or per measurand is available on the Scatter tab.
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Figure 94: Charts and tables – Youden plot – Scatter
11.7 Histogram and normal plot The Histogram and normal plot window displays the graphics of the histogram and the normal plot for one selected ring test-sample-measurand combination. The charts are displayed on separate tabs. Click on the corresponding tab to select a chart. The toolbar contains buttons for editing or printing the charts as well as drop-down menus for selecting the ring test, sample and measurand. With the histogram the underlying statistical distribution of the measurement errors can be identified visually, and additionally a statistical test (Chi-square-test) for normal distributions is provided. If the p value presented in the figure is smaller than 0.05 it can be concluded that the assumption of normal distribution can be denied at the significance level of 5 %. It has to be noted that the test result is strongly dependent on the possible existence of outliers. Hence it is possible to exclude all measurement values with an absolute value of the Z score higher than 3 (|Z score|
