Dr. Young's LabAnnemarie Reardon, Dissertation.
Two previous studies found that Seasonal Affective Disorder symptoms co-vary across remission in individuals with SAD (Young & Schmitt, 2000) and in individuals with a broad range of seasonality (Reardon & Young, 2003). Using a within-subjects factor analysis of daily symptom ratings, these studies found that SAD symptoms clustered into three factors: energy/motivation, cognitive/affective, and appetite. Further examination of the energy/motivation factor, found one- and two-phase symptom courses were common among these individuals and that, for a majority of participants, there was an alteration in the course of symptoms around the Spring Equinox.
The current study replicated and extended these studies by examining the additional factors of cognitive/affective and appetite symptoms. In the context of the Dual-Vulnerability Model (Young, et al., 1999), we examined the patterns of symptom offset for the cognitive/affective and appetite factors to determine whether (1) these factors exhibit one- and two-phase symptom courses and (2) changes in vegetative symptoms precede changes in cognitive/affective symptoms. Multiphase regression analysis was used to trace the time courses of symptoms across the period of expected remission.
Similar to our previous study, both one- and two-phase symptom courses were observed for the cognitive/affective and appetite factors. An alteration, or two-phase symptom course, occurred for all three factors and, for the Cognitive/Affective factor, two-phase symptom courses occurred significantly more often than one-phase courses. Contrary to expectations, changes in energy/motivation and appetite factors (i.e., vegetative symptoms) did not precede changes in cognitive/affective symptoms. Also, no evidence was found for a relationship between winter seasonality and symptom course.
Combined with earlier, this study suggests that both one- and two-phase symptom courses may be common across the full range of seasonality, from little or no effect of seasonal change to a diagnosis of SAD. Our failure to find the predicted temporal relationship among symptom groups might be because the onset and offset of a disorder could entail different mechanisms. Another explanation might be the broad range of seasonality among our participants. Individuals with a diagnosis of SAD might prove a more reliable test of the theory.