Contraceptive effectiveness as a function of desired family size

The inclusive notion of method acceptability has been used as an explanation of variation in willingness to use contraception, the regularity with which contraception is used, and the effectiveness of contraception in preventing pregnancy. With the additional assumption that variation in method acceptability is related to differential motivations to limit numbers and control spacing, two hypotheses are advanced. (1) As the number of children individual couples desire is approached or achieved in practice, the proportion attempting fertility control increases. (2) The success with which fertility is controlled improves as fertility approaches the number of children desired. These hypotheses are supported strongly by data. Several implications of these relationships are advanced.