Optimal scoring of the Multidimensional Pain Inventory in a chronic pain sample.

The Multidimensional Pain Inventory (MPI) is one of the most commonly used self-report instruments in pain settings. The MPI can be used to classify patients into three clusters or its nine scales can be treated as dimensions in efforts to understand patient heterogeneity. Previous research suggests the existence of a fourth cluster, whose members have been labeled 'repressors,' that emerges with the addition of a defensiveness scale to the MPI. The current paper compared the abilities of MPI cluster and dimensional models with and without a measure of defensiveness to capture variability in validating variables related to personality, psychopathology, physical functioning, and treatment outcome in a chronic pain sample. Results suggest that dimensional models consistently outperform cluster models in explaining variance in outcome variables, and that the addition of a measure of defensiveness increments the validity offered by the MPI scales. Implications for the assessment of pain patients are discussed.