WHICH ENVIRONMENTAL VARIABLES ARE RELATED TO THE ONSET OF SEASONAL AFFECTIVE-DISORDER

The regular fall-winter onset of seasonal affective disorder is believ ed to be related to seasonal changes in the environment. However, the high correlation among various environmental variables has made it dif ficult to distinguish which ones may Play a causal role. Photoperiod s hould explain variations in onset risk across both latitude and day of the year because it varies as a function of only these 2 factors. In Study 1, the authors found this to be the case using data from 5 locat ions. Environmental factors that vary from year to year should explain variations in onset risk across both time of year and actual year. In Study 2, the authors examined data from 7 years at 1 location and fai led to fmd evidence of this effect for daily hours of sunshine, mean d aily temperature, and total daily radiation. Findings support photoper iod as being related to the onset of seasonal affective disorder.