Some of the methods originally used to find relationships between reliability and power associated with a single measurement are extended to difference scores. Results, based on explicit power calculations, show that augmenting the reliability of measurement by reducing error score variance can make significance tests of difference more powerful.…

Two articles discuss the controversy about the relationship between reliability and the power of significance tests in response to the discussion of Donald W. Zimmerman, Richard H. Williams, and Bruno D. Zumbo. Lloyd G. Humphreys emphasizes the differences between what statisticians can do and constraints on researchers. Zimmerman, Williams, and…

Two methods--non-distributional and normal--are derived for estimating measures of pass-fail reliability. Both are based on the Spearman Brown formula and require only a single test administration. Results from a simulation (n=20,000 examinees) and a licensure examination (n=4,828 examinees) illustrate these methods. (SLD)