Parkes, A; Wight, D; Henderson, M; Stephenson, J; Strange, V; (2008) Contraceptive Method at First Sexual Intercourse and Subsequent Pregnancy Risk: Findings from a Secondary Analysis of 16-Year-Old Girls from the RIPPLE and SHARE Studies. Journal of Adolescent Health , 44 (1) 55 - 63. 10.1016/j.jadohealth.2008.06.006. Green open access