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Test-retest reliability evaluates the extent to which a psychological measure yields consistent scores when administered to the same individuals across different times. This form of reliability is crucial when assessing constructs that are theoretically expected to remain stable, such as intelligence or self-esteem. However, it is not an appropriate standard for constructs that naturally vary over time, like mood or immediate stress levels.

Test-Retest Reliability

Test-retest correlation is the statistical coefficient calculated between two sets of scores from a measure administered at different times. A test-retest correlation of $$+.80$$ or greater is generally considered to indicate good reliability for constructs expected to be stable. For example, the Rosenberg Self-Esteem Scale demonstrated a highly reliable test-retest correlation of $$+.95$$ when administered to students twice, a week apart.

Test-Retest Correlation

Assessing test-retest reliability involves measuring the same group of participants at two separate times and calculating the correlation between their scores. This statistical relationship is commonly visualized using a scatterplot. Since standard research designs often only test participants once, researchers might specifically design a two-phase study for a new measure to evaluate this reliability. Alternatively, data from a study designed to answer a different research question can be utilized if the measure was administered multiple times. For instance, if an instructor measures students' attitudes at the start and end of a semester to detect learning changes, the correlation between those two sets of scores can simultaneously be used to assess the measure's test-retest reliability, even if no overall attitude change occurred.

Assessing Test-Retest Reliability

A measurement tool can yield highly consistent results without actually measuring the intended construct. For instance, attempting to measure a person's self-esteem by using a ruler to measure their index finger length would demonstrate excellent test-retest reliability, as finger length is stable over time. However, this method would have absolutely no validity, as finger length has no conceptual relationship to self-esteem.

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