Zelnik M, Kantner J F
Fam Plann Perspect. 1977 Mar-Apr;9(2):55-6, 58-63, 67-71.
The prevalence of sexual activity among never-married U.S. teenage women increased by 30 percent between 1971 and 1976; so that by age 19, 55 percent have had sexual intercourse. The increase, which has occurred at all ages and among all races, has been accompanied by a dramatic increase in the use of contraception, the use of the most effective methods, and the more regular use of all methods. Nevertheless, few teenagers begin use of contraception at the same time that they initiate intercourse--and many wait until after they have experienced pregnancy.
1971年至1976年间，美国未婚少女的性活动发生率增长了30%；到19岁时，55%的少女有过性交经历。这一增长在所有年龄段和所有种族中都有发生，同时伴随着避孕措施使用的显著增加，最有效方法的使用增加，以及所有方法使用的更加规律。然而，很少有青少年在开始性交的同时就开始使用避孕措施——而且许多人会等到怀孕后才采取措施。
