populasi sampel

Chapter 8 Population & Sampling

Sampling •

Selecting a group of people, events, behaviors, or other  elements with which to conduct a study.

Sample •

The selected group of  people (or elements) from which data are collected for a study.

Population •

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The entire set of  individuals individu als (or elements) who (that) met the sampling criteria. Also called target population

Accessible Population •

The portion of the target population to which the researcher has reasonable access.

Element •

An individual unit of a population. •

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Person (subject) Event Behavior 

Sampling Criteria •

The characteristics essential for  inclusion in the target population •

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Between the ages of 18 and 45 Ability to speak English Admitted for gall bladder surgery Diagnosed with diabetes within last month

Representativeness •

The sample, the accessible population, and the target population are alike in as many ways as possible.

Representativeness •

Needs to evaluate: •

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Setting Characteristics of the subjects: age, gender, ethnicity, income, education Distribution of values on variables measured in the study

Sampling Error  •

Definition: Difference between the population mean & the mean of the sample

Sampling Error  Sampling Error 

Sample

Population

Population Mean

Sample Mean

Sampling Error  •

Random Variation •

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The expected difference in values that occurs when different subjects from the same sample are examined. Difference is random because some values will be higher and others lower than the average population values.

Sampling Error  •

Systematic Variation (Bias) •

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Consequence of selecting subjects whose measurement values differ  in some specific way from those of  the population These values do not vary randomly around the population mean

Sampling Frame •

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A listing of every member of  the population, using the sampling criteria to define membership in the population. Subjects are selected from the sampling frame.

Sampling Plan •

Outlines strategies used to obtain a sample for a study: •

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Probability sampling plans Nonprobability sampling plans

Probability Sampling •

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Simple Random Sampling Stratified Random Sampling Cluster Sampling Systematic Sampling

Probability (Random) Sampling Methods •

Simple Random Sampling

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Stratified Random Sampling

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Cluster Sampling

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Systematic Sampling

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Random Assignment to Groups

Nonprobability (Nonrandom) Sampling •

Convenience (Accidental Sampling)

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Quota Sampling

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Purposive Sampling

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Network Sampling

Factors Influencing Sample Size •

Effect Size

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Type of Study Conducted

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Number of Variables

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Measurement Sensitivity

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Data Analysis Techniques

Power Analysis •

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Standard Power of 0.8 Level of Significance •

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Effect Size •

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alpha = .05, .01, .001 .2 Small; .5 Medium; .8 Large

Sample Size

Example Sample •

A convenient sample of 55 adults scheduled for first-time elective CABG surgery without cardiac catheterization, catheterization, who had not had other major surgery within the previous year, and who were not health professionals met the study criteria and were randomly assigned to one of two instruction conditions...

Example Sample •

Based on a formulation of 80% power, a medium critical effect size of 0.40 for each of the dependent variables, and a significance level of  .05 for one-tailed t-tests means, a sample size of 48 was deemed sufficient to test the study hypotheses...

Example Sample •

There were 21 men and 4 women in the preadmission group; 2 subjects were black...The majority (85%) of  the subjects in both groups g roups reported moderate incomes (Rice et al., 1992)

Critiquing the Sample •

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Identify the sample criteria Judge the appropriateness of  the sampling criteria Identify the sampling method Was the sample heterogeneous or homogeneous?

Critiquing the Sample •

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Was the sample size identified? Was the percent of subjects consenting to participate addressed? Was the sample mortality identified? Was the sample size adequate?

Critiquing the Sample •

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Did the researcher r esearcher successfully successfully implement the sampling plan? How effective was the sampling plan in achieving representativeness? In what ways was the sample not representative?

Critiquing the Sample •

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Were there possibilities of  biases in the sample? Were subjects selected from a sampling frame? Was random sampling used?

Critiquing the Sample •

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Were any power analyses reported? Is there a possibility of  a Type II error related to any of the findings? f indings?