Table 1.
Measures and assessment schedule
| Measure | Construct assessed | Metric | Pre-TX | Weekly during TX | Mid-TX* | Post-TX* | Winter 2 | Winter 3 |
|---|---|---|---|---|---|---|---|---|
| SIGH-SAD [42] (see description) | SAD recurrence (primary outcome) and remission status, symptom severity | Categorical recurrence status, categorical remission status, score | X | X | X | X | X | X |
| Beck Depression Inventory-II (BDI-II) [52] | Depression symptom severity, remission status (BDI-II ≤ 8) | Score, categorical remission status | X | X | X | X | X | X |
| Beck Anxiety Inventory [53] | Anxiety symptom severity | Score | X | X | X | X | X | |
| Dim light melatonin onset (DLMO) | Circadian timing | Clock time (military) | X | X | X | X | ||
| Wrist actigraphy and Pittsburgh Sleep Diary [54] | Sleep & circadian timing; daytime activity | Mean mid-point of sleep; mean daily activity count | X | X | X | X | ||
| †Phase angle difference (PAD) | Circadian timing | DLMO–mid-sleep (from actigraphy) | X | X | X | X | ||
| †PIPR | Post-illumination pupil response | Net PIPR (red–blue light response) | X | X | X | X | X | |
| ‖Pupil dilation and sustained frontal gamma-band EEG responses to negative and winter words | Prefrontal engagement as it relates to emotion elaboration and regulation | Mean pupillary and sustained frontal gamma responses 2–10 s following emotional word onset | X | X | X | X | X | |
| ‖Seasonal Beliefs Questionnaire (SBQ) [32] | Maladaptive thoughts about the seasons and light availability | Score | X | X | X | X | X | |
| ‖Dysfunctional Attitudes Scale-Form A (DAS) [55] | Depressive schemas | Score | X | X | X | X | X | |
| ‖Behavioral Activation for Depression Scale (BADS) [56] | Self-reported behavioral activation | Score | X | X | X | X | X | |
| †Composite Scale of Morningness (CSM) [57] | Chronotype | Score | X | X | X | X | X | |
| Treatment Credibility Scale [58] | Credibility for the CBT-SAD and LT treatment conditions | Score | X | X | X | |||
| Millon Clinical Multiaxial Inventory—Fourth Edition (MCMI-IV) [59] | DSM-5 personality disorders | Scale scores, possible DSM-5 personality disorders | X | |||||
| Quality of Life Enjoyment and Satisfaction Questionnaire (Q-LES-Q) [60] | Quality of life related to: physical health, mood, leisure time activities, social relationships, general activities, work (if applicable), household duties (if applicable), and school/coursework | Score | X | X | X | X | ||
| Sheehan Disability Scale (SDS) [61] | Mental-health related impairment in work, social life/ leisure activities, and home life/family responsibilities | Score | X | X | X | X | ||
| MOS SF-20 (62) | Health-related quality of life | Score | X | X | X | X | ||
| SCID-5-RV major depressive episode criteria | Recurrences between post-treatment and winter 2 and between winters 2 and 3 | Categorical recurrence status | X | X |
*Repeated in winter 2 if switched to the alternate treatment
†Candidate mediator of LT’s effects
‖Candidate mediator of CBT-SAD’s effects. TX-treatment