statistical analysis

Analysis of Medical Data Research Perspective

Nancy B. Clark. M.Ed. Director of Medical Informatics Education FSU College of Medicine Spring 2004

http://www.med.fsu.edu/informatics

Objectives 



Review statistical concepts to be on Step 1. Determine what data exist relative to a clinical question or formal hypothesis  

use IT to locate existing data sources identify and locate existing data sets  



Within institution Outside institution

Analyze, interpret and report findings 





Select and use appropriate computer software: Excel, SPSS Use software to perform simple statistical analysis and portray results graphically Interpret reports

Prerequisite Skills (Step 1 USMLE) •

Fundamental concepts of measurement • •

• • • •

•

Scales of measurement Distribution, central tendency, variability, probability Disease prevalence and incidence Disease outcomes (eg, fatality rates) Associations (correlation or covariance) Health impact (eg, risk differences and ratios) Sensitivity, specificity, predictive values

More Prerequisite Skills (Step 1 USMLE) 

Fundamental concepts of hypothesis testing and statistical inference  



Confidence intervals Statistical significance and type I error Statistical power and type II error

More Step 1 Topics 

Fundamental concepts of study design  

 

 

Types of experimental studies (eg, clinical trials, community intervention trials) Types of observational studies (eg, cohort, casecontrol, cross-sectional, case series, community surveys) Sampling and sample size Subject selection and exposure allocation (eg, randomization, stratification, self- - selection, systematic assignment) Outcome assessment Internal and external validity

Scales of Measure 





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Nominal – qualitative classification of equal value: gender, race, color, city Ordinal - qualitative classification which can be rank ordered: socioeconomic status of families Interval - Numerical or quantitative data: can be rank ordered and sizes compared : temperature Ratio - interval data with absolute zero value: time or space

Distribution, Central Tendency… Mean

…Variability, Probability… 

   

Mean Median Mode Standard deviation Statistical Significance p < .01

Confidence Interval

Statistical Significance Type I and Type II errors Null Hypothesis = Ho

Reject Ho

Ho True

Ho False

Type I error

Correct decision

Do Not Reject Ho Correct decision

Type II error

Statistics Online Textbook 



The Statistics Homepage http://www.statsoftinc.com/textbook/stathome .html

Disease Prevalence and Incidence 

Prevalence 





probability of disease in entire population at any point in time 2% of the population has diabetes

Incidence 



probability that patient without disease develops disease during interval 0.2% or 2 per 1000 new cases per year

Sensitivity, Specificity 



sensitivity = a / (a+c) specificity = d / (b+d)

Patients with disease Test is positive Test is negative

Patients without disease

a

b

c

d

Predictive Value 







Positive predictive value = a / ( a+b) Negative predictive value = d / (c+d) Post-test probability of Test is disease given positive positive test = a / (a+b) Post-test probability of disease given negative Test is test = c / (c+d) negative

Patients with disease

Patients without disease

a

b

c

d

Good Resource Sen, Spc, PV 



An Introduction to Information Mastery http://www.poems.msu.edu/InfoMastery/defa ult.htm 

Diagnosis   



Sensitivity and specificity Predictive values Likelihood ratios

InfoRetriever 

Calculators: Epidemiology, Diagnostic test

Fundamental Concepts of Study Design 

Good Resource   



Epidemiology for the Uninitiated BMJ Online Textbook http://bmj.com/collections/epidem/epid.shtml

Finding Health Statistics

Types of Health Statistics Questions 

  

Fact lookups Research Presentations Social and Policy indicators

Strategies for Finding Health Stats 

 

Use Portal Start at Internet site Start with book or article

Internet Portals of Health Stats 

Lists of links that provide starting points for browsing or searching  





Keyword search in portal vs Google General idea what you want

The Related Health Services Research Web Sites http://www.nlm.nih.gov/nichsr/hsrsites.html The NCHS portal: http://www.cdc.gov/nchs/

Other Statistical Web Sites 

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CDC Data and Statistics http://www.cdc.gov/scientific.htm FedStats Home Page http://www.fedstats.gov/ Compare these two U Michigan’s Statistical Resources on the WEB – HEALTH What type of stats

Lexis-Nexis Statistical Universe 

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Subscription resource Searches stat data   



Subject List Limit search Reports or tables

http://web.lexisnexis.com/statuniv?B1=Connect+to+Statistic al+Universe

MMWR 

   

Morbidity – illness Mortality – death http://www.cdc.gov/mmwr/ Disease Trends Tables - searchable

Health Care Data 

      

Healthcare Cost and Utilization Project HCUPnet Hospital discharges Ambulatory service Costs Amount of care By diagnosis and procedure Surveys of hosp, physicians, nursing homes

Health Consequences 

    

Costs to society, individuals Cost from care Costs of illness Impact on infrastructure HCFA=>CMS Health Accounts http://www.cms.hhs.gov/statistics/nhe/default. asp

State and International Data 

   

Floridahealthstat.com - Where Florida Health Data Resides DOH Epidemiology KFF State Health Facts Online United Nations Statistics Division World Health Organization Research Tools

Individual Datasets 

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EMR Billing CDCS Customized data collection tools

Data Analysis

Selecting the Appropriate Software 

Spreadsheet 

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Numerical (interval or ratio) data Sums Averages Standard deviations Simple charts and graphs

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Statistical Software  

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Nominal or Ordinal data Comparisons of two+ groups Frequency tables Complicated charts and graphs Normal curves Class intervals Statistical significance

Spreadsheets 

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Excel Pocket Excel

Data Tables 

 

Field names at top Each row is a record (sample) Sorting whole table  



By one column By more than one column

Sorting individual sections

Descriptive Statistics 

Distribution  



frequency distribution Histogram

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 

Central tendency   

Mean Median mode

Dispersion



 

Range Standard deviation Variance

N Not P (inferential stats)

Central Tendency 

Mean 



Median 



=MEDIAN(A2:A7)

Mode 



=AVERAGE(b2:b1500)

=MODE(A2:A7)

N  

=COUNT(A2:A1500) =COUNTBLANK(A2:B5)

Dispersion 

Range 



Standard deviation 



=MAX(A2:A60)- MIN(A2:A60) =STDEV(A2:A110)

Variance 

=VAR(A2:A110)

Distribution 

Frequency distribution   



Not easy – use SPSS FREQUENCY(data_array,bins_array) Use help

Histogram 

Bar chart of frequency table

Hands on experience 

Analyze data in examples2.xls

Statistical Software Intro to SPSS

Statistical Software 

  

SPSS Provided by request/justification Lab Computers Start => Programs => SPSS for Windows => SPSS 11.0 for Windows

Start Screen 



Don’t show this dialog in the future. OK

Open Breast Cancer Survival

Data View

Views

Variables View

File Information 

 

Utilities Menu File Info… Output window

Descriptive Statistics 

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Analyze Menu Descriptive Statistics Frequencies Select Age ► Click Statistics button In Central Tendency 

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Mean, Median, Mode

In Dispersion 

Standard Deviation, variance



In Percentile Values 

 

Quartiles

Continue OK

Graphing 

Graphs Menu 



 

Pie…

Summary for Groups of cases Lymph Nodes ► OK

Histogram with Normal Curve 

Graphs Menu 

 



Histogram..

Select Age ► Check Display Normal Curve OK

Simple Correlation Analysis 



Age and Tumor Size Analyze Menu 

Correlate… 



  

 

Bivariate

Select Age ► Select Pathological Tumor Size ► Check Pearson and Spearman – Two tailed OK Is there a correlation? Negative or Positive? Is it statistically significant?

Save Output 

  

Save on All Users drive Under Nancy.clark SPSS Output Files Name it your name: ie, KerryBachista.spo

Importing Data 





From Excel, SAS, dBase, etc. Variable names first row File Menu, Open 



Files of Type 

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Data… Excel

Tutorial, Samples 

Demo.exe



  

Type in Labels Pick Type of variable Enter Value Labels Etc.

SPSS Tutorials 

 

In the Help Menu On Informatics Web page Books: 

Statistics for Social & Health Research (Sage) 



Argyrous, George

Statistics Applied to Clinical Trials (Klawer Academic Publishers) 

Cleophas, Ton J., et al

Objectives 

Determine what data exist relative to a clinical question or formal hypothesis  

use IT to locate existing data sources identify and locate existing data sets  



Within institution Outside institution

Analyze, interpret and report findings  



Select appropriate computer software: Excel, SPSS Use software to perform simple statistical analysis and portray results graphically Interpret reports

Questions?