Incremental validity of the Ego Impairment Index: a re-examination of Dawes (1999).

This article examined the incremental validity of the Ego Impairment Index (EII), a Rorschach measure of cognition, perception, and reasoning. R. M. Dawes (1999) borrowed 2 previously published data sets to assess the incremental validity of the EII. Dawes determined that in order for the EII to be considered a valid measure, the overall EII score should "outperform" 2 of the variables that compose the index. Using this approach, Dawes reported that the EII had "deficient" (p = .059) incremental validity. In this study, the incremental validity of the EII was re-examined using 1 of the data sets used by R. M. Dawes (1999). Applying the same strategy as Dawes, the author tested the incremental validity of the EII in predicting positive symptoms of schizophrenia, a more appropriate and clinically relevant criterion measure of impairment. The EII significantly predicted positive symptoms (p < .005) even after the 2 EII variables selected by Dawes and the measure of social competence were 1st entered into the equation. The results suggest that the EII adds meaningful information in the assessment of thought disturbance.