# Test-retest reliability

## Assess the stability of a survey outcome across time

Test-retest reliability is a form of reliability that assesses the

**stability and precision of a construct across time**. There is a**baseline**or "**pretest**" administration of the survey and then a "**post-test**" administration of the same survey after a predetermined period of time or intervention. Essentially, test-retest reliability measures the**stability**of scores across time. If scores from both administrations are highly correlated with stable scores and error variances across time, then**evidence**of test-retest reliability is assumed. Pearson's r is used to establish evidence of test-retest reliability.### Phenomena that affect test-retest reliability

There are certain phenomena associated with test-retest reliability that may grossly affect the stability of survey scores across time:

1. The

2. The sample of individuals should be relatively

3. Due to both systematic and unsystematic error in measurement and the general variance and diversity in populations, some measures and constructs will be more

1. The

**length of time**between administrations cannot be too short, nor too long. Base decisions on the time difference within the context of your research question. What amount of time is feasible for purposes of testing stability in this context? Most researchers use between**one and six weeks**of time between administrations. Time lapses of**six months**are considered too excessive to obtain a stable measure of effect.2. The sample of individuals should be relatively

**homogenous in regards to demographic, confounding, clinical, and prognostic factors**. People change differently according to their physiological and psychological development.3. Due to both systematic and unsystematic error in measurement and the general variance and diversity in populations, some measures and constructs will be more

**unstable**across time than others.### The steps for conducting test-retest reliability in SPSS

1. The data is entered in a within-subjects fashion.

2. Click

3. Drag the cursor over the

4. Click on

5. Click on the baseline observation, pre-test administration, or survey score to highlight it.

6. Click on the

7. Click on the second observation, post-test administration, or survey score to highlight it.

8. Click on the

9. Click

2. Click

**.**__A__nalyze3. Drag the cursor over the

**drop-down menu.**__C__orrelate4. Click on

**.**__B__ivariate5. Click on the baseline observation, pre-test administration, or survey score to highlight it.

6. Click on the

**arrow**to move the variable into the**Variables:**box.7. Click on the second observation, post-test administration, or survey score to highlight it.

8. Click on the

**arrow**to move the variable into the**Variables:**box.9. Click

**OK**.### The steps for interpreting the SPSS output for test-retest reliability

1. In the

If the

If the

**Correlations**table, match the row to the column between the two observations, administrations, or survey scores. The**Pearson Correlation**is the test-retest reliability coefficient, the**Sig. (2-tailed)**is the*p*-value that is interpreted, and the**N**is the number of observations that were correlated.If the

*p*-value is**LESS THAN .05**, and the Pearson correlation coefficient is above 0.7, then researchers have evidence of test-retest reliability.If the

*p*-value is**MORE THAN .05**, or the Pearson correlation coefficient is below 0.7, then researchers do not have evidence of test-retest reliability.Click on the

**Principal Components Analysis**or**Validity**button to continue.## Hire A Statistician - Statistical Consulting for Professionals

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