An age-period-cohort analysis for prevalence of common psychiatric disorders in Japan, 1999–2017

Purpose: This study aimed to analyze the prevalence of common psychiatric disorders in Japan via an age-period-cohort (APC) analysis. Methods: Data were used on the prevalence of schizophrenia, schizotypal, and delusional disorders; mood [affective] disorders (mood disorders, hereafter); and neurotic, stress-related, and somatoform disorders from the 1999–2017 Patient Survey in Japan. The age group was defined as 20–89 years with 5-year increments; the cohort was assigned for each age group of each year with a 1-year shift. A Bayesian APC analysis was used to decompose changes in prevalence into three effects: age, period, and cohort. Results: The APC analysis revealed that the peaks of age effect varied among sexes and diseases. The period effects for all the diseases showed increasing trends over the analyzed years. Although the cohort effect for the prevalence of schizophrenia, schizotypal, and delusional disorders increased until the 1960s, it decreased afterwards. On the other hand, the cohort effects for the prevalence of mood disorders and neurotic, stress-related, and somatoform disorders increased from around the 1950s, and it indicates the prevalence increased particularly in young ages over the years. Also, the trends of each effect were relatively similar between mood disorders and neurotic, stress-related, and somatoform disorders. Conclusion: Increase in public awareness and psychological stress associated with a change in a social environment is thought to affect the period and cohort effects on the prevalence of mood disorders and neurotic, stress-related, and somatoform disorders.