Date of Completion


Document Type

Honors College Thesis


Psychological Science

Thesis Type

Honors College, College of Arts and Science Honors

First Advisor

Kelly Rohan

Second Advisor

Richard Norton

Third Advisor

Timothy Stickle


cognitive-behavioral therapy, light therapy, seasonal affective disorder, mood, depression, weather


The current study examined the relationship between weather variables and mood in the context of a randomized clinical trial comparing two first-line treatments for seasonal affective disorder (SAD; N = 177 adults): SAD-tailored cognitive-behavioral therapy (CBT-SAD) and light therapy. Weather variables included daylength, temperature, precipitation, sky cover, solar radiation, and wind speed at the study site corresponding to date of mood assessment. Regression analyses tested the predictive effect of each weather variable, treatment condition, and their interaction on depression severity at post-treatment and at follow-ups one and two winters after treatment. Weather variables were hypothesized to affect mood, with more pronounced effects for light therapy participants, particularly at Winter 2 follow-up where the parent study found superiority of CBT-SAD over light therapy. For Structured Interview Guide for the Hamilton Depression Rating Scale-SAD Version (SIGH-SAD) scores, daylength and a wind speed X treatment interaction were predictive at post-treatment, and sky cover was predictive at Winter 1 follow-up. For Beck Depression Inventory-Second Edition (BDI-II) scores, daylength and temperature were predictive at post-treatment, and daylength and solar radiation were predictive at Winter 2 follow-up. In the light therapy group, each unit increase of wind speed at and above 8.03 knots was associated with a decrease of 2.43 points on the SIGH-SAD at post-treatment. All models controlled for pre-treatment depression scores, which accounted for much of the variance in later depression scores at each timepoint. CBT-SAD was associated with significantly lower depression severity at Winter 2 than light therapy, even after adjusting for pre-treatment depression severity and each weather variable, bolstering the primary efficacy results of the parent study.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.