Seasonality in affective disorders in Switzerland.

Objective: To estimate the prevalence of seasonal affective disorder (SAD) and its subsyndromal form (S-SAD) in Switzerland (47°N). Method: A representative sample from all three language areas of Switzerland (n = 980) were given a structured telephone interview using the extended Seasonal Pattern Assessment Questionnaire (SPAQ+ ). A smaller, hut also representative sample in the city of Basel filled in the SPAQ+ form as well as undergoing a structured diagnostic interview. Results: In this Swiss sample, 2.2% of the population presented with symptom severity of SAD. 8.9% with S-SAD. In Basel, a much higher prevalence of SAD was found. Seasonal problems occurred more often in patients with the Diagnostic and Statistical Manual (DSM)-III diagnosis of major affective disorders than in those with pure anxiety disorders or no psychiatric diagnosis Conclusion: These estimates for SAD in Switzerland are similar to those found in the Zurich Study, using other methods, and for populations in the UK, with the limitations inherent in retrospective I questionnaire studies.