Discriminant validity of the illness behavior questionnaire and Millon Clinical Multiaxial Inventory-III in a heterogeneous sample of psychiatric outpatients.

The discriminant validity of measures of abnormal illness behaviors and psychopathology 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 Questionnaire (IBQ; Pilowsky & Spence, 1994), while the Millon Clinical Multiaxial Inventory-III (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 of the IBQ scales, suggesting discernible discriminant validity. However, the lack of discrimination between groups on several of the MCMI-III scales raises questions about the test validity of this multidimensional instrument.