A comparison of clinically and empirically derived MMPI groupings in low back pain patients.

Two methods of grouping MMPI scales were employed with 271 patients who were attending a Back Clinic at a university hospital. One method involved clinically derived decision rules, while the other utilized a multivariate clustering procedure. Five subgroups of patients were identified with each method. Both procedures showed subgroup differences in terms of pretreatment pain intensity, activity limitations, McGill affective scores, and physician ratings of degree of functional impairment; the elevated subgroups showed more dysfunction. Follow-up comparisons revealed that, regardless of the classification procedure used, the elevated subgroups showed poorer response to treatment. Only the clinically derived groupings had significant differences in chronicity of pain and total scores on the McGill Pain Questionnaire. On the other hand, only the statistically based system showed significant differences on age and marital status. Furthermore, only the statistical system identified subgroups of male patients that predicted followup pain intensity decreases in a manner that indicated clinical usefulness.