The Health Behaviour in School-Aged Children (HBSC) survey aims to obtain insight and improve the understanding of young peoples' health behaviour and well-being. Although not a purposeful feature of the study design, in 2002 the Irish HBSC data was collected towards the end of the academic year (Spring/Summer) and at the start of the next school year (Autumn/Winter).

Seasonality has been documented in the literature as an influence on health status and behaviours. 1,2 On the basis of such associations, it was both necessary and opportunistic to use the dual intake of the Irish HBSC data collection, to examine the presence of seasonal effects in the self-reported health status and health behaviour of Irish adolescents.

Results:
Male participants from the Spring/Summer intake were significantly more likely to have tried smoking, to eat supper on the weekends, to be on a diet and to use a bicycle helmet frequently, than those from Autumn/Winter. However, the partial Eta squared effect sizes (ES) were .004, .004, .003 and .005 respectively.
Girls surveyed in Autumn/Winter ate fruit more frequently (ES=.003) than those surveyed in Spring/Summer. Conversely girls from the first intake drank coke/soft drinks (ES=.006), exercised (ES=.002) and wore a bicycle helmet (ES=.003) more frequently than students from the second intake.