The article extends and applies previous approaches by Klauer and Fischer to the statistical evaluation of ability changes in tests conforming to the Rasch model (RM). Exact uniformly most powerful unbiased (UMPU) hypothesis tests and uniformly most accurate (UMA) confidence intervals (CIs) for the amount of change can be constructed for each testee separately. Under the H-0 of no change, the individual p values of testees can be aggregated also within groups. The current results extend this method by an estimator for a group effect, an exact UMPU test of its significance, a corresponding UMA CI, and a likelihood ratio test for group comparisons. All these methods are applied to two sets of data concerning a highly controversial issue in literature: the so-called Mozart Effect (ME). As test material, a unidimensional test of spatial ability by Gittler and Arendasy was presented to two samples of testees (Studies I and II). On the basis of these data, the occurrence of a short-term effect of the experimental condition can be demonstrated which, however, seems to be related to the relaxation between pretest and posttest rather than to the musical priming.
