Standardized conditional SEM: A case for conditional reliability

An examinee-level (or conditional) reliability is proposed for use in both classical test theory (CTT) and item response theory (IRT). The well-known group-level reliability is shown to be the average of conditional reliabilities of examinees in a group or a population. This relationship is similar to the known relationship between the square of the conditional standard error of measurement (SEM) and the square of the group-level SEM. The proposed conditional reliability is illustrated with an empirical data set in the CTT and IRT frameworks.