A longitudinal investigation of seasonal variation in mood

A prospective panel study was conducted to measure seasonality of mood in a random community sample in Melbourne, Australia (N = 245). Based on resear ch into the structure of human mood, it was predicted that a lowering of mo od in winter relative to summer would be observed in positive affect (PA) a nd behavioral engagement (BE), but not negative affect (NA). These variable s were measured across summer and winter for 3 years. Consistent with the m ajority of research in the Northern Hemisphere, analyses on the entire samp le found evidence of a small prospective season effect on the BE scale (exp laining 2.1% of variance in BE scores). Also, as expected, no season effect was seen on the NA scale. In the entire sample, the season effect was not significant for PA, but joint factor analysis of the BE, PA, and NA scales confirmed that the season effect seen in the BE scale-was largely due to it ems that were pure measures of PA. Winter pattern seasonality was both reli able across measures and significantly more marked among the subgroup of re spondents who self-identified winter pattern of mood on the Seasonal Patter n Assessment Questionnaire.