An investigation of the existence of distinctive MMPI-2 profiles in three diagnostically different samples

Abstract

[Abstract]: Medico-legal examination of people who have suffered physical or psychological injuries usually involves the assessment of psychological adjustment post-injury. An assumption that appears prevalent in the research literature, is that individuals with the same organic or psychological disorders will form relatively homogeneous groups, and hence exhibit similar patterns of test performance. In essence this assumption underlies the notion that clinical group means accurately reflect the behaviour of the individuals that constitute different diagnostic groups. Four studies were undertaken in this study. The first study examined the cluster patterns of MMPI-2 test performance in a medico-legal sample (n = 197) of individuals suffering Chronic Pain. Study two investigated MMPI-2 cluster patterns in a medicolegal sample of individuals (n = 200) who had suffered a Traumatic Brain Injury. The third study examined distinctive MMPI-2 cluster profiles in a medico-legal sample of individuals (n = 132) suffering Post Traumatic Stress Disorder. The final study compared the results of the previous investigations to determine whether there was any communality in the cluster profiles found in the three diagnostically different samples. Both hierarchical (Ward’s Method), and k-means cluster analysis procedures were employed to identify the number of clusters, and common patterns of MMPI-2 test performance in the three aforementioned forensic samples. Results indicated that multiple profiles (three to four) exist within the each of the three different diagnostic groups. The profiles, however, indicated that a single pattern of MMPI-2 performance does not appear to be characteristic of a particular disorder. The notion of homogeneity of test patterns (as far as the MMPI-2 is concerned) within a diagnostic group was not supported. The MMPI-2 profiles identified in each of the clinical classifications were not found to be specific to these forensic samples, and commonly occurred across the three diagnostic groups. Cluster analysis appeared to be a useful methodology to determine commonly occurring profiles within a specified population. A considerable number of elevated responses, however, were noted for the Within Normal Limits (WNL) profiles. This classification may be somewhat of a misnomer, due to high numbers of individuals still indicating difficulties. The current findings highlight the complexity of attempting to classify individual patterns of MMPI-2 test performance in terms of a single diagnostic category, and directly challenge the utility of the MMPI-2 as an effective tool in this regard.