Resolving the test–retest agreement or reliability dilemma

Abstract

Agreement refers to the degree to which an individual i’s test scores match in test–retest settings. Agreement has been thought to be unapproachable with correlational reliability indices. Stable unstable reliability theory extends Spearman’s reliability model and specifies the probability that i’s test–retest true scores match. Thus, agreement and reliability are simultaneously addressed. Two examples, one using longitudinal data, illustrate the procedure.