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Pre-employment Psychological Testing of Police Officers: The MMPI and the IPI as Predictors of Performance

NCJ Number
204582
Author(s)
Kimberly D. Simmers; Thomas G. Bowers; James M. Ruiz
Date Published
2003
Length
18 pages
Annotation
This study reviewed research on the Minnesota Multiphasic Personality Inventory (MMPI and MMPI-2) and the Inwald Personality Inventory (IPI) to determine whether there is a difference between the ability of the two instruments to predict the future performance of police officers.
Abstract
The MMPI/MMPI-2 has been one of the most commonly used personality measures in the pre-employment test of applicants for policing. In 1989 the original MMPI was revised (MMPI-2) to improve validity and acceptability. The IPI was developed specifically for application with law enforcement officers in response to criticism of the MMPI's application to officer selection. The IPI scales measure both personality characteristics and behavioral patterns. The scales contain critical items used to identify disturbed individuals as well as items that identify less pathological personality and adjustment problems. Research studies on the two instruments were selected from published and unpublished sources from 1980 to 2000 and focused on the prediction characteristics of the instruments. The studies selected were also required to have official departmental documentation of officer behavior and to provide statistical information on the relationship between the predictor at issue and the dependent variable that could be converted into Pearson's "r" as well as a corresponding effect size. Of the studies found, 18 met the criteria. Pearson product-moment correlation coefficients were produced for all predictors in each study that reported a numerical relationship with the criterion. Next, the obtained correlations were transformed into effect sizes by using Friedman's (1968) formula. A mean correlation and a mean effect size were calculated for the MMPI/MMPI-2; and a mean correlation and a mean effect size were calculated for the IPI. An independent groups "t" test was performed to compare the mean correlation and mean effect size of the two instruments and job performance. The findings show that both MMPI versions and the IPI provided modest correlation and effect size relationships to police behavior. The IPI scores, however, yielded significantly higher relationships between instrument results and subsequent police performance. Although additional studies are required to confirm these findings, the results argue for the increased use of the IPI, at times in combination with the MMPI-2. 6 tables and 51 references