Oedegaard, O. Psych Quar (1945) 20: 381. doi:10.1007/BF01574330
A total of 14,231 first admissions to Norwegian mental hospitals for the period of 1926 through 1935 are examined, and incidence rates by age, sex and diagnosis are determined. From these incidence rates, the expectations of the various forms of mental diseases are calculated. Different types of expectations and statistical methods are discussed, and the results of some authors compared. The objections generally voiced against the use of statistical information on hospital admissions as a basis for the determination of the incidence of mental disease in the average population are partly exaggerated, and in part the difficulties can be overcome by the use of adequate statistical methods. The expectations, arrived at by this “census method” form a valuable supplement to those obtained by the “direct method” generally used in psychiatric studies of heredity, and are, under favorable circumstances, even preferable as controls for investigations according to the sib method.
Methods of determining the number of mentally ill persons alive at any given time are discussed; and the results obtained by one method are given. Finally the age distributions of certain psychoses are illustrated by incidence rates based upon the age at onset of the first symptoms.