First incidence depression in the Lundby Study: a comparison of the two time periods 1947-1972 and 1972-1997

Abstract

Background: The Lundby Study is a prospective, longitudinal study on a total population consisting of 3563 subjects during 50 years. This study compares first incidence rates of depression and cumulative probabilities for developing a depression over the two time periods 1947-1972 and 1972-1997.

Method: The Lundby Study started in 1947. Follow-ups were carried out in 1957 and in 1972. In 1997 the surviving subjects (N=1797) were interviewed by psychiatrists with a semi-structured interview. Best-estimate consensus diagnoses were used and ICD-10 and DSM-IV diagnoses were added. Further, 1030 subjects who had died during the last follow-up period 1972-1997 were investigated.

Results: Women had higher incidence rates than men in both periods. The average annual incidence rate was lower for women and tended to be lower for men 1972-1997 as compared with 1947-1972. The cumulative probability for developing a depression was 22.5% for men and 30.7% for women 1972-1997. In 1947-1972 the corresponding figures were 22.8% in men and 35.7% in women.

Limitations: The recall period is of considerable length, probably introducing recall bias. The inter-rater reliability over 50 years is fairly acceptable concerning depression.

Conclusion: Lower annual standardised incidence rates were seen in 1972-1997 compared with 1947-1972. These findings suggest that the trend of increasing rates of depression in the Lundby cohort has terminated. Incidence rates and cumulative probabilities to develop a depression were higher for women than for men, indicating that gender differences continue to play a role.