THE POWER OF RASCH PERSON-FIT STATISTICS IN DETECTING UNUSUAL RESPONSE PATTERNS

Five Rasch person-fit indexes were compared on their ability to detect spuriously high and low nonsystematic response patterns. The moderati ng effects of test dimensionality, type of misfit, and test length wer e also investigated. Results indicated that (1) all fit indexes were n ot significantly correlated with Rasch trail estimates; (2) their samp ling distributions deviated significantly from the standard normal dis tribution; (3) using adjusted cutoff criteria to identify misfit, ECI2 (Z), ECI4(Z), l,(z) and WSR-C performed equally well in the detection of misfit regardless of test dimensionality, type of misfit, and test length (however, only I, is recommended for the spuriously high respon se patterns for a two-dimensional test); (4) the false positive rate f or each index was less than the nominal .05 level; (5) Rasch person-fi t indexes are more sensitive to spuriously high response patterns than to spuriously low response patterns on a two-dimensional test, but wh en the test is unidimensional they demonstrate equal sensitivity to bo th types of misfit; and (6) the detectability of misfit increases with test length.