As we saw in my previous post, when we look at the largest Protestant denominations, we see that there is an obvious linear relationship between family size and the decline or growth of a denomination. When we add other large religious categories to the figure, however, the relationship becomes less obvious. The correlation certainly still exists, but we see more examples of denominations where the previous generation had fairly large families, but they nonetheless failed to grow or even saw a decline.
For example, the big Pew religious survey that was released this year showed that Mormons actually declined slightly as a percentage of the U.S. population between 2007 and 2014. Mormons are famously fecund, and my examination of survey data showed that they had, on average, larger families than any other group I considered. While the LDS church is still comparatively healthy, a rather high apostacy rate is the only thing that can account for this finding.
Catholics are another group that exhibited comparatively high fertility rates among older women, yet they have also declined as a percentage of the U.S. population. Understanding the dynamics of Catholicism in the U.S. is somewhat trickier, as the U.S. has seen a steady influx of immigration from predominantly Catholic countries for many decades. Without this knowledge, one might infer that the Catholic Church is fairly healthy. This would be an incorrect inference. Given the extraordinary number of Catholic immigrants who have entered the country since 1965, and fairly healthy Catholic birthrate, it is a sign of weakness that the percentage of Americans who identify as Catholic has not increased since the 1970s, and has even declined somewhat. Again, this implies that Catholics have a huge problem with apostacy. According to Pew, about 32 percent of Americans were raised Catholic, but only about 21 percent of Americans identify as Catholic today.
To avoid the headaches that come from looking at the rates of Catholic identification among the entire U.S. population, it is useful to look at what percentage of non-Hispanic white Americans identify as Catholic, and how this has changed over time. We see this in the figure below (from the GSS). We see that white Catholic identification has declined steadily since the mid-1980s, and shows little sign of reversing.
What accounts for this finding? My initial guess was that the major scandals in the Catholic church about sex abuse were the catalyst for an exodus from the church. However, this decline began before the most damning stories were uncovered, and the rate of decline did not seem to pick up after those revalations. So something else must be at work.