Despite the classic single case studies of multiple personality disorder by Ludwig et al. (1972) and Larmore et al. (1977) and more recent descriptive and psychophysiological studies of larger series of multiple personality (Bliss, 1980; Horevitz & Brown, 1984; Kluft, 1984a, b, 1985; Putnam, 1984; Putnam et al., 1983), much of the literature on the disorder consists of parital, single clinical case reports from which sweeping conclusions are drawn.

We describe the application of ESM, a new behavioral time-sampling method, to the assessment of rapid mood, self-perceptual, and clinical state changes in a woman with multiple personality disorder. The purpose of the study was to examine the utility of experiential sampling in the study of a clinical syndrome characterized by frequent, rapid state changes (switching of multiple personality alternates) that were readily apparent to the treating psychiatric staff but were of uncertain periodicity in non-clinical, everyday situations. We also wished to make a contribution to the systematic study of the phenomenology of multiple personality disorder.

ESM permits comparison of a naturalistically derived sample of the patient's own experience with clinical observations, standardized single-time-of-day rating instruments, and psychophysiological and other laboratory measures. Subjects collect data about their own experience at different times during the day. ESM can help characterize clinically significant, within-day variations in mood, behavior, and experience such as the immediate precipitants of switch processes or mood changes.