Cluster analysis of insomniacs' MMPI profiles: relation of subtypes to sleep history and treatment outcome.

The Minnesota Multiphasic Personality Inventory (MMPI) profiles of 100 insomniacs who presented for treatment at a university medical center were analyzed by a hierarchical clustering procedure. This analysis revealed two major personality types that accounted for 88% of the sample. The two types referred to as "Type 1" and "Type 2" insomniacs differed significantly in regard to sleep history questionnaire responses and responsivity to treatment. MMPI scales and sleep history questionnaire items suggested that Type 1 insomniacs were less defended, more aroused/activated, and had sleep histories characterized by more childhood sleep problems and greater difficulties with sleep-disruptive cognitions than did Type 2 patients. Further, Type 1 patients had a poorer response to behavioral treatment as measured by change in sleep-onset latency than did Type 2 patients. These results suggest that the MMPI may be useful in identifying distinctive personality subgroups among insomniacs. Treatment implications are discussed, and mechanisms underlying the group differences are considered.