First incidence depression in the Lundby Study: A comparison of the two time periods 1947-1972 and 1972-1997.
Mattisson C, Bogren M, Nettelbladt P, Munk-Jorgensen P and Bhugra D;
Commented by , 21 Sep 2005
Background
The World Health Organization (WHO) found that unipolar major depression was the fourth leading cause of disability adjusted life years (DALY) in 1990 and has estimated that depression rises to the second leading cause of DALY in 2020.
This estimate is built on findings of an increasing incidence rate of depression since World War II. However, only few longitudinal studies on the incidence of depression have been undertaken, and results have often been influenced by methodological drawbacks.
Methods
The Lundby study was started in 1947 in the Lundby area in the south of Sweden, and the follow-up period is now 50 years. 2550 subjects were originally included, and subsequently newcomers to the area have been included.
In the present paper, incidence rates of depression were compared for the two time periods 1947-1972 and 1972-1997 using the same semi-structured interview and adding diagnoses of ICD-10 and DSM-IV. Only depression of medium and severe degree of impairment was included.
Results
The average annual incidence rate of depression for men was 3.3/1000 years in 1947-1972 and 2.8 /1000 years in 1972-1997. For women, the rates were 5.5/1000 years in 1947-1972 compared with 4.1/1000 years in 1972-1997.
Professor Kessing's comments
This is an important and impressive study undertaken throughout 50 years. The diagnostic criteria for depression used in the study has remained the same over the years. Furthermore, the researchers who undertook the field work in 1972 were supervisors for the new interviewers thus improving the continuity of the method.
The results suggest that the trend of increasing rates of depression has terminated in Sweden as lower rates were found for both men and women in recent times.
Due to the length of the follow-up, recall bias can never be excluded in longitudinal studies. In the Lundby study, multiple sources of information such as case notes, registers and key-informants may have helped to reduce recall bias.
The Lundby criteria for depression seem to correspond quite well with the DSM-IV diagnoses for major depression, and in the present publication inter-rater reliability tests demonstrated a satisfactory ability to distinguish the healthy from the sick.
The incidence rates reported in the Lundby study is similar to the rate in the ECA Baltimore follow-up study (ref. 1), but much lower than the rates in the NEMESIS study (ref. 2). However, the higher rates found in the NEMESIS study may be due to a short follow-up time of only 1 year.
Although methodological explanations of the decreasing incidence rates can not be excluded, other explanations seem reasonable to consider. A possible explanation may be that health has increased in Sweden due to a better socio-economic status in 1972 than previously.
In the period from 1947 to 1997 several changes have been taken place in the Swedish society such as urbanization, changes in family structure, institutionalization of care for children, etc. It does not seem based on the present results that such factors may increase stress or the susceptibility to stress and increase the risk of developing depression eventually.
References
1. Eaton WW, Anthony JC, Gallo J, Cai G, Tien A, Romanoski A, Lyketsos C and Chen LS. Natural history of Diagnostic Interview Schedule/DSM-IV major depression. The Baltimore Epidemiologic Catchment Area follow-up. Archives of General Psychiatry 1997; 54 (11); 993-999
2. Bijl RV, De Graaf R, Ravelli A, Smit F and Vollebergh WA. Gender and age-specific first incidence of DSM-III-R psychiatric disorders in the general population. Results from the Netherlands Mental Health Survey and Incidence Study (NEMESIS). Social Psychiatry and Psychiatric Epidemiology 2002; 37 (8); 372-379