Abstract

PIP: With the use of a relatively new multivariate life table technique, 1st year contraceptive use failure rates are calculated for currently married U.S. women, based on data from the 1973 and 1976 National Surveys of Family Growth, conducted by the National Center for Health Statistics. When, in order to delay or prevent a subsequent pregnancy, age and family income are controlled for simultaneously, the pill is considered the most effective method with a 1 year standardized failure rate of 2.4%, next is the IUD with 4.6%, the condom (9.6%), spermicides (17.9%), diaphragm (18.6%), and natural family planning (NFP) or rhythm (23.7%). Including other variables, such as parity, education, age at marriage, religion, and race, does not result in any significant improvement in the ability to predict contraceptive use effectiveness beyond that obtained by using method, intention, age, and income. Previous studies, which did not employ multivariate techniques found that women who sought to prevent another pregnancy were less likely to experience contraceptive failure than were those who sought only to delay conception, presumably because preventers are more highly motivated to avoid conception. This analysis, however, shows that among those 25 and younger, preventers have higher failure rates for each method than delayers. The most likely explanation for this phenomenon is that women who had all the children they wanted at an early age have probaly already had previous contraceptive failures, while those who are still spacing at older ages are more likely to have been successful in postponing pregnancy until the desired time. Among preventers, failures for all methods decline with increasing age. By contrast, among delayers, failure rates (except for those among condom users) are lowest for women ages 22-25 and differ little among older and younger women. It is notable that failure rates among pill users are generally very low for women in all age, income, and intention groups. The highest failure rate for pill users (8% for women under age 22 seeking to prevent an unwanted pregnancy and who have annual family incomes of under $10,000) is the same as the lowest failure rate for women who depend on NFP methods (those seeking to avoid an unwanted pregnancy who have incomes of over $15,000 and are age 30 or older). For women under age 22, the diaphragm is associated with extremely high failure rates, but diaphragm use improves at older ages. Among women age 30 and older, the condom is associated with lower failure rates than any method except the pill. Failure rates shown are based on those experienced in actual use and reflect failures due to the method itself as well as to incorrect use. If theoretical method effectiveness is measured as the lowest failure rate seen by any subgroup of women under age 30, rates for each method are: pill--1.2%, IUD--2.3%, condom--5.7%, spermicides--9.4%, diaphragm--9.7%, and rhythm--12.6%. For each method, the lowest rates are obtained by preventers with annual family incomes of over $15,000 and ages 26-29. (author's modified)