Discriminant validity at the illness behavior questionnaire and millon clinical multiaxial inventory-ill in a heterogeneous sample of psychiatric outpatients

The discriminant validity of measures of abnormal illness behaviors and psy chopathology was examined in three samples differing in illness proneness: a sample of young healthy university students (n = 38), a general community sample (n = 36). and a sample of clinical psychiatric outpatients (n = 36) . Adjustment to illness was measured using the Illness Behaviour Questionna ire (IBQ, Pilowsky & Spence. 1994). while the Millon Clinical Multiaxial In ventory-ill (MCMI-III; Millon. 1994) was used to measure clinical syndromes and personality MANCOVAs were performed across the three groups on the IBQ and the MCMI-III categories, separately. As expected, clinical outpatients obtained significantly higher scores than did nonclinical groups on most o f the IBQ scales, suggesting discernible discriminant validity. However, th e lack of discrimination between groups on several of the MCMI-III scales r aises questions about the test validity of this multidimensional instrument . (C) 2000 John Wiley gi Sons, Inc. J Clin Psychol 56.779-791, 2000.