Repeatability - Psychological Testing

Psychological Testing

Since the same test is administered twice and every test is parallel with itself, differences between scores on the test and scores on the retest should be due solely to measurement error. This sort of argument is quite probably true for many physical measurements. However, this argument is often inappropriate for psychological measurement, since it is often impossible to consider the second administration of a test a parallel measure to the first.

The second administration of a psychological test might yield systematically different scores than the first administration due to the following reasons:

1. The attribute that is being measured may change between the first test and the retest. For example, a reading test that is administered in September to a third grade class may yield different results when retaken in June. We would expect some change in children’s reading ability over that span of time, a low test-retest correlation might reflect real changes in the attribute itself.

2. The experience of taking the test itself can change a person’s true score. For example, completing an anxiety inventory could serve to increase a person’s level of anxiety.

3. Carryover effect, particularly is the interval between test and retest is short. When retested, people may remember their original answer, which could affect answers on the second administration.