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

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.