The Impact of Latitude on the Prevalence of Seasonal Depression

BACKGROUND: This study sought to determine whether the prevalence of the seasonal subtype of major depression (SAD) in the community varied as a function of latitude. METHODS: Random telephone numbers were generated across 8 degrees of latitude (41.5 degrees N to 49.5 degrees N) for the province of Ontario. Eight strata of 1 degree each were sampled equally throughout a 12-month period. Using a validated and structured diagnostic interview, we …