Assessing Trends in the Desire to Avoid Pregnancy: A Cautionary Note.

The desire to avoid pregnancy-to delay the next birth or have no further births-is a fundamental sexual and reproductive health indicator. We show that two readily available measures-prospective fertility preferences and the demand for contraception [Demand] construct-provide substantially different portraits of historical trends. They also yield correspondingly different assessments of the sources of contraceptive change. We argue, with supporting empirical evidence, that Demand enormously overstates the historical trend in the desire to avoid pregnancy because Demand as currently constructed is in part a function of contraceptive prevalence. This makes for "reverse causality" in decompositions of contraceptive change, producing an upward distortion on the order of 25 percentage points in the amount of contraceptive change attributed to a change in fertility desires. Decomposition of contraception change free of the distortion reveals that contraceptive change has been due almost entirely to more complete implementation of fertility preferences. This is explained in part by the surprisingly slight historical change in preferences, a fact we document and then show is a consequence of a historical shift in parity composition toward lower parities.