[fractaled]

I read that to mean there was only one study that was randomized & controlled.

Basically when you say "there are studies that show X" you aren't saying anything because "studies" are cheap unless your methodology is rigorous and sound, which isn't the case a lot of the time.

[leereeves]

Of course. Here are three randomized, controlled studies just from the first page of the Google Scholar results:

http://archpsyc.jamanetwork.com/article.aspx?articleid=20429...

http://ajp.psychiatryonline.org/doi/full/10.1176/ajp.2006.16...

http://archpsyc.jamanetwork.com/article.aspx?articleid=20433...

Apparently, 91 papers passed Nussbaumer et al's assessment of the abstract (and were presumably randomized, controlled trials):

We assessed 91 full-text papers for inclusion in the review, but only one study providing data from 46 people met our eligibility criteria.

Those eligibility criteria were:

For efficacy, we included randomised controlled trials on adults with a history of winter-type SAD who were free of symptoms at the beginning of the study.

I think it may have been the focus on prevention (rather than treatment of symptomatic depression) that excluded all the other papers.

I just skimmed the paper the paper the first time and didn't notice that the authors were searching for studies of a very specific question: prevention (excluding treatment) of seasonal affective disorder (excluding any other form of depression).