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Much psychiatric morbidity is chronic and extends over large segments of the individual's life-span. A major impediment to obtaining accurate and complete knowledge of the natural history of mental disorder has been the difficulty in obtaining adequate data. The case register method is potentially useful in filling this need. The essential theoretical features of the case register which distinguish it from other techniques are: (1) Total populations can be studied as well as selected or random samples; (2) Unlike indexes and other data-collection systems, data are individual rather than event-orientated; (3) Data collection is systematic and standardized rather than haphazard and heterogeneous, so tha