title: Seasonal affective disorder in Australia: is photoperiod critical?
abstract: OBJECTIVE
  Seasonal affective disorder (SAD) is a variant of recurrent depression in which episodes are linked to a particular season, typically winter. SAD is understood as the extreme end of a continuum of seasonality in the general population. Photoperiod (the timing and duration of daylight) has been assumed to be aetiologically critical. The present research used a survey design to investigate the assumed centrality of photoperiod for SAD/seasonality in Australia. Two hypotheses were tested: that self-reported seasonality does not increase further from the equator and that seasonality does not stand alone from non-seasonal neurotic complaints.
  
  
  METHODS
  The sampling frame used was adult females on the Australian Twin Registry roll. A sample of 526 women residing across the latitudes of Australia responded to a survey based around the Seasonal Pattern Assessment Questionnaire (SPAQ). The SPAQ asks respondents to retrospectively report on season-related changes in mood and behaviour. The survey also contained three questionnaire measures of neurotic symptoms of anxiety and depression: the General Health Questionnaire (GHQ), the Community Epidemiological Survey for Depression (CES-D) and the State-Trait Anxiety Inventory-Trait (STAI-T).
  
  
  RESULTS
  Self-reported seasonality did not correlated with latitude (r = 0.01, NS). On the other hand, a substantial relationship was found between seasonality and each of the measures of non-seasonal complaints: GHQ (r = 0.35, p < 0.001); CES-D (r = 0.35, p < 0.001); and STAI-T (r = 0.30, p < 0.001).
  
  
  CONCLUSIONS
  Within the limitations of a design based on retrospective self-report, the findings of the present study suggest that the diathesis for SAD/seasonality may not be photoperiod-specific. At least in Australia, there is provisional support for the proposal that human seasonality may have a broader psychological component. The findings are discussed in terms of established research into normal mood, trait personality and non-seasonal depression.
authors.affiliation: Department of Psychology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: G W
authors.initials: GW
authors.lastname: Murray
authors.forename: D A
authors.initials: DA
authors.lastname: Hay
mesh_terms: D000293:Adolescent; D000328:Adult; D001315:Australia / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008027:Light; D008875:Middle Aged; D012189:Retrospective Studies; D016574:Seasonal Affective Disorder / Q000453:epidemiology* / Q000523:psychology; D014427:Twins / Q000523:psychology