Context: The causes of the substantial increase in contraceptive prevalence in developing countries since 1960 have been intensely debated. An important unresolved issue concerns the relative contributions of changes in fertility preferences (such as increases in the proportion of women who want no more children) versus improved implementation of established preferences (such as increased contraceptive use among women who do not want another child).

Methods: Contraceptive prevalence data from the World Fertility Surveys and Demographic and Health Surveys for 26 countries in Latin America, Asia and Africa from the 1970s to the 1990s are analyzed through regression decomposition. The aim is to determine how much of the change in prevalence can be attributed to changes in fertility preferences (referred to as "composition") and how much is due to changes in rates of contraceptive use within preference categories ("rates").

Results: The substantial increases in contraceptive prevalence in the period since the 1970s in Latin America, Asia and Africa were less the result of increased demand for smaller families and more the result of the satisfaction of existing demand. The rates component dominated in all 26 countries, representing more than 70% of the increase in contraceptive prevalence in 24 countries and exceeding 80% in two out of three. Only in Ghana and Ecuador did the composition component account for one-third or more of the increase in prevalence, while at the other extreme, changes in preferences constituted less than 10% of the increase in prevalence in
Colombia, Peru, Thailand, and Zambia. This implies that most of the observed increase in contraceptive prevalence would have occurred even if there had been no change in couples' fertility preferences. In Sub-Saharan Africa, changes in fertility preferences accounted for more of the increase in contraceptive prevalence than in other regions.

Conclusions: The findings are consistent with the premise that has justified the investment in family planning programs in many countries during the past three decades. Moreover, they undercut arguments that dismiss the potential for producing substantial increases in prevalence by satisfying existing demand for fertility regulation. Possible reasons for the increased implementation of preferences include improved access to contraceptive supplies or the reduction of costs not directly related to contraceptive access (such as cultural, social and health concerns).