Many studies on the fertility differential by religion have considered both Catholics and Protestants to be equally homogenous groups. Contrary to these studies, we contend that Protestant fertility must be studied in the context of heterogeneous groups. Specifically, conservative Protestantism, with its beliefs about artificial birth control mirroring Catholic teaching, should be examined separately from other Protestant traditions. Using data from the General Social Survey we find that conservative Protestants and Catholics had about the same level of fertility, while mainline Protestants have a fertility rate that is significantly lower than that of Catholics. We also examine the changes in these differences over time
