Appropriate interpretation of assessment data requires an appreciation that tools are subject to measurement error. School psychologists recognize, at least on an intellectual level, that measures are imperfect--that test scores and other quantitative measures (e.g., rating scales, systematic behavioral observations) are best estimates of…

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…

There is great controversy in the field of learning disabilities (LD) regarding the establishment of criteria for LD identification. The traditional approach to LD identification is to use the IQ-discrepancy. Lyon and colleagues (2001) point out the numerous problems with such an approach, including faulty assumptions about the adequacy of an IQ…