Date of Award


Document Type


Degree Name

Master of Arts (MA)



First Advisor

Kelly J. Rohan

Second Advisor

Jane Okech


Sudden gains, large between-observation symptom improvements during treatment, are associated with better acute and follow-up outcomes in cognitive-behavioral therapy (CBT) for mood and anxiety disorders. Using the group CBT for seasonal affective disorder (CBT-SAD) condition (n=88) from a parent randomized clinical trial comparing CBT-SAD and light therapy, this study examines whether sudden gains can be detected in CBT-SAD and whether they relate to outcome at post-treatment and at follow-ups one and two winters later. Sudden gains were detected by applying Kelly et al.’s (2005) criteria to week-to-week symptom changes [i.e., scores on the Structured Interview Guide for the Hamilton Rating Scale for Depression—Seasonal Affective Disorder Version (SIGH-SAD)] during CBT-SAD. Using SIGH-SAD score drop > 6, 44.3% (39/88) of CBT-SAD participants had a sudden gain. More than half of all sudden gains (25/39, 64.1%) occurred between pre-treatment and Week 2. Sudden gainers had lower depression severity on the Beck Depression Inventory-Second Edition (BDI-II) and a greater likelihood of remission (BDI-II < 8) at both winter follow-ups than non-gainers. Sudden gain groups did not differ on post-treatment depression outcomes. Relative to non-gainers, sudden gainers showed greater improvement in seasonal beliefs, CBT-SAD’s potential mechanism, during CBT-SAD, with more flexible seasonal beliefs than non-gainers at post-treatment. Membership in a particular CBT-SAD group was not related to the effect of sudden gains on treatment outcome. This study contributes to the literature regarding the impact of sudden gains on cognitive processes, extends the sudden gains literature to a new treatment (CBT-SAD), and is the first to consider the influence of group membership on sudden gains.



Number of Pages

39 p.

Available for download on Friday, June 12, 2026