Recent attention to causes of seasonality of births leads to an interest in seasonality patterns in the antecedents to birth, including gestational length, conception, and coital activity. In this paper we study the beginning of the process: first intercourse among adolescents and young adults. Analysis of a small and local dataset is suggestive that loss of virginity is particularly likely during the summer. A test of this "Summer Vacation Theory" using a large national dataset supports the generality of the phenomenon. Further, a prediction that seasonality patterns will change during the transition from high school to work and college is tested and supported. The existence of both biological and psycho-social mechanisms is suggested. Policy implications are reviewed.
PIP: Longitudinal data on 1405 female teenagers attending 4 junior high schools in Tallahassee, Florida in 1980-82 (Adolescent Sexuality dataset [ADSEX]) and on 4013 female youth throughout the US (National Longitudinal Survey of Youth [NLSY]) were studied to examine seasonality patterns of 1st intercourse. ADSEX student data revealed an overall peak in June which continued throughout July and August. This was the case for both whites and blacks as well as males and females. 29% reported 1st sexual intercourse during June and July (17% expected). 46% had 1st coitus between May-August (expected 33%). These results suggest the Summer Vacation Theory, which was tested with the more representative NLSY data. NLSY data demonstrated the same patterns of 1st coitus as did the ADSEX data. The NLSY analysis resulted in a significant rejection of uniform onset across months (p.0001). The peak for Hispanics occurred in May-June rather than June-July, however. 1 possible reason for seasonality of 1st sexual intercourse was a biological mechanism--an increase in libido as temperature rises. A psychosocial mechanism was tested and it was found that the peak among 19-23 year olds was still in the summer months, but the peak was less pronounced. The seasonality difference between 13-18 year olds and 19- 23 years olds was significant (p.005). This strengthened the hypothesis that the transition from pre- to post-high school is a cultural marker and that socio cultural mechanisms play a role in the observed summer seasonality patterns. These results indicate that sex education in April may be more relevant than sex education in the beginning of the school year. Sex education programs should take into account the differences between Hispanic and other youth, and youth leaders should consider these results when organizing summer activities.