The Symptom Structure of Seasonal Affective Disorder: Integrating Results from Factor and Network Analyses in the Context of the Dual Vulnerability Model

Research on seasonal affective disorder (SAD) has produced several etiological models of SAD symptomatology, including a common cause model that conceptualizes symptoms as the result of a single underlying disease process and the Dual Vulnerability Model (Young et al., Journal of Affective Disorders, 22, 191–197 1991) which posits that cognitive/affective symptoms of depression are responses to vegetative symptoms (fatigue, hypersomnia, increased appetite) in individuals with a cognitive vulnerability to these seasonal changes. This study used exploratory factor analysis and network analyses to examine 22 symptoms of winter SAD in 177 adults at the start of a randomized SAD treatment trial (Rohan et al., American Journal of Psychiatry, 172, 862–9 2015). The factor analysis supported a novel four-factor model that included Negative Cognition, Loss of Vitality, Increased Appetite/Weight and Dysregulation across symptom domains. The results of the network model of interacting symptoms paralleled those of the factor analysis in producing four clusters of inter-correlated symptoms. A directed acyclic graph was constructed to model possible causal relations between symptom factors/clusters. Results suggest that vegetative symptoms (Loss of Vitality and Appetite/Weight) contribute to Dysregulation and that Loss of Vitality and Dysregulation contribute to Negative Cognition, supporting the overall structure of the Dual Vulnerability Model but with greater symptom differentiation. Findings have implications for how SAD should be researched (e.g., clusters vs. diagnosis or individual symptoms), opportunities for intervention, and the expected course of onset and remission.