On the Quantum and Tempo of Fertility: Reply

BEFORE EXPLAINING why we disagree with the views expressed in the two preceding comments, we summarize briefly the purpose and main features of the method described in Bongaarts and Feeney (1998). Our study set out to address a well-known flaw in the total fertility rate, the most widely used measure of period fertility. The TFR is affected by changes in the timing of childbearing. In years when women's ages at childbearing rise, the TFR is depressed, and in years when timing of child-bearing is advanced, the TFR is inflated relative to the level that would have been observed without such timing changes. To remove the distortions in the TFR caused by these tempo effects, we proposed a simple equation for calculating an " adjusted " total fertility rate (TFR'). Details are provided in our original 1998 article and in Bongaarts (1999), but we briefly reiterate a few key points. First, TFR' should be interpreted as a variant of the conventional TFR. The TFR is defined as the number of births women would have by the end of their childbearing years (i.e., completed fertility) if the age-specific fertility rates observed in a given year applied throughout the childbearing years. This is a hypothetical rate because no actual cohort will experience these observed period fertility rates. Our TFR' is a similar hypothetical measure, but one that corrects for distortions caused by year-to-year tempo changes. Neither the TFR nor the TFR' attempts to estimate the completed fertility of any actual birth cohort, nor do they attempt any prediction of future fertility. Our goal is simply to provide a period measure of fertility that removes tempo distortions in conventionally calculated total fertility rates. Second, our study was inspired by the work of Norman Ryder, and we gratefully acknowledge his fundamental contribution to this line of research. However, our conceptualization of quantum and tempo is different from Ryder's. In his work, quantum refers to the completed fertility of cohorts,