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On the basis of two EEG sleep criteria, REM latency and REM activity, the authors achieved 81% accuracy in distinguishing between 47 patients with primary depression and 48 patients with secondary depression using discriminant analysis. Sleep efficiency, the percentage of delta sleep, and the percentage of REM sleep discriminated between psychotic and nonpsychotic subgroups in the group with primary depression with 75% accuracy. REM activity and intermittent nocturnal awakening accurately discriminated two subtypes of patients with secondary depression at a level of 81%. These results suggest that EEG sleep measurements can yield significant data to aid in differential diagnosis in psychiatry.
Kupfer et al. (Sun,) studied this question.