Stability of patient adaptation classifications on the multidimensional pain inventory

This study examined the adaptational classification stability of the multidimensional pain inventory (MPI) in two samples of female fibromyalgia syndrome patients. Retest resulted in one-third of patients being assigned to a different classification. Twenty patients had four repeated MPI assessments over a 10-month period; 85% of them changed classification at least once. Prediction of classification stability using demographic variables and measures of pain, depression, anxiety, impression management, and self-deception was unsuccessful. Examination of the MPI Variable Response Scale and an index of the goodness of fit of the cluster for each patient did not yield sufficient predictive power. The implication of this study is that for a sizable number of chronic pain patients, MPI classifications may not be stable, trait-like characterizations. As such, caution must be applied when treatment is tailored to MPI clusters and when classification change is used as an outcome measure.