[1] Univ Western Ontario, Dept Psychol, London, ON N6A 5C2, Canada
[2] Univ Western Ontario, Dept Obstet & Gynaecol, London, ON N6A 5C2, Canada
[3] Indiana Univ Sch Med, Dept Pediat, Sect Adolescent Med, Indianapolis, IN 46202 USA
[4] Indiana Univ, Dept Sociol, Bloomington, IN USA
[5] Indiana Univ, Kinsey Inst Res Sex Gender & Reprod, Bloomington, IN USA
[6] New England Res Inst, Watertown, MA 02172 USA