Decreasing first-admission rates of schizophrenia among males in Denmark from 1970 to 1984. Changing diagnostic patterns?

The first-admission diagnoses of schizophrenia in males aged 15 years and over for the 15-year interval 1970-84, based on annual reports from the Danish Psychiatric Register, showed a highly significant decrease from 12.6 to 8.5 per 100,000, amounting to 37% by regression analysis. The decrease is almost entirely caused by the age group 15-24 years, in which the incidence fell from 30.7 to 14.6 per 100,000. During the same period a remarkable increase in the corresponding first-admission rates of "borderline states" (ICD-8: 301.83, Danish version) and paranoid and unspecified psychoses (ICD-8: 297, 298.9, and 299) was observed, particularly for the age groups 15-24 and 25-34 years. Changes in diagnostic habits accounting for the decreasing schizophrenia incidence among males are discussed.