Decreases in depression over 20 years in a mining area of Sardinia: due to selective migration?

BACKGROUND: The objective of the study was to determine if community surveys, conducted 3 times over a period of 20 years in a small district of Sardinia (Italy), confirm the increase in depressive disorders reported in the recent literature.
METHODS: Three community surveys were carried out on randomized samples of the same Sardinian mining area in 1988, 1998 and 2008. The surveys were conducted using the interview "Present State Examination" in 1988 (depression diagnosed with ICD-IX) and the CIDI-S in 1998 and 2008 (major depression diagnosed with ICD-X). The three surveys produced estimates of one-month prevalence and of lifetime prevalence in 1998 and 2008.
RESULTS: Our work found a substantial decrease in depressive disorders from the survey conducted in 1998 to the survey in 2008 using a similar methodology, except in the youngest age group, which showed an increase in the rate. A decrease in the frequency of depressive disorders compared to what was found 20 years ago was also observed. However, in this case the comparison is more problematic because of use of different diagnostic systems. DISCUSSION: The research seems to show a decrease in depressive disorders over the past two decades. While the small population examined makes it difficult to generalize the overall findings, this study suggests that the hypothesis of an increase in the incidence of depressive disorders since the 1980s in western countries, should have exceptions. A complex interaction between socio-economic (mining closure and large migration) and biological factors (possible selective migration) is likely to influence changes in the prevalence of mood disorders. However, due to certain limitations of this study, this hypothesis may be considered from a heuristic perspective.