The development and progression of winter depression and the effect of
light therapy was assessed in 31 of 83 subjects who reached a Beck De
pression Inventory (BDI) score of 15 (indicating severe depression) an
d were consequently given light therapy. The subjects were regularly e
valuated with the BDI at 2-week intervals during the months before and
after light therapy. The BDI score increased rapidly during the 4 wee
ks before treatment and fell immediately after treatment. A marked dec
rease in depression score was also seen with the Hamilton Depression R
ating Scale (HDRS) and HDRS/SAD extension rating scale. Although light
therapy had a beneficial effect in most of our subjects, it had littl
e or no beneficial effect in a subgroup of non-responders, possibly be
cause of a difference in the nature of the depression suffered.