| Abstract: | Contraceptive effectiveness is conventionally measured by a pregnancy rate, which reveals little about the way in which pregnancy risks vary among couples. In this paper a technique is presented for estimating curves of pregnancy risk. The technique is applied to data from the Family Growth in Metropolitan America study for purposes of estimating how much these couples would have to Improve their initial contraception In order to realize, by contraception alone, the calibre of family limitation claimed by respondents late in their childbearing period. A very substantial improvement Is estimated as necessary. It Is also argued that the notable increase In contraceptive effectiveness before and after second birth, observed for couples desiring only two children is attributable mainly to a more regular practice of contraception. Changes Iin method preference, decline in average fecundabillty and increased contraceptive skill are viewed as secondary factors. |
