Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Terry Rabinowitz



Seasonal affective disorder (SAD) is characterized by annual recurrence of clinical depression in the fall and winter months. The importance of SAD as a public health problem is underscored by its high prevalence (an estimated 5%) and by the large amount of time individuals with SAD are impaired (on average, 5 months each year). The specific cause of SAD remains unknown; however, researchers have identified possible chronobiological and psychological vulnerabilities to SAD. The study aimed to clarify psychological and chronobiological correlates of SAD in the first test of an integrative model of SAD.

The project used a longitudinal design to test the respective contributions of the chronobiological and cognitive vulnerabilities on winter depression severity in 31 SAD patients and 33 never-depressed controls at sites in Burlington, VT and Pittsburgh, PA. The measures selected for the cognitive vulnerability were established measures of vulnerability to nonseasonal depression with empirical support for their relevance to SAD: brooding rumination, dysfunctional attitudes, cognitive reactivity to an induced sad mood, and season-specific cognitions. The chronobiological vulnerability was measured as Phase Angle Difference (PAD) and deviation from PAD of 6 hours. All measures were completed once in the summer, when the SAD patients were remitted, and once in the winter, when patients were clinically depressed. Patients were distinguished from controls on most cognitive vulnerability measures (brooding, as well as rumination, dysfunctional attitudes, and seasonal beliefs). SAD patients exhibited shorter PAD than controls, but did not exhibit greater deviation from PAD-6. Results provide further support for specific cognitive, but not chronobiological, vulnerabilities in prediction of SAD. Limitations of the current sample are discussed.

Results hold implications for future SAD research bridging the chronobiological and psychological disciplines with the ultimate aim of improved understanding, assessment, treatment, and prevention of SAD.



Number of Pages

211 p.