In a previous post I noted the reasonably strong correlation between birthrates and the changing size of different Christian denominations. Those denominations that had a large number of large families tended to be the denominations that are shrinking at a lower rate.
That correlation was pretty strong, but some more evidence will be useful to strengthen the case for such a relationship.
Today I want to turn to trends within a particular denomination. The Lutheran Church- Missouri Synod helpfully provided me with membership data for each of its North American districts over the last several decades.
The LCMS does not provide data on fertility and marriage for its members. However, we can look at the general patterns in each of those districts overall. The LCMS districts do not perfectly correspond to state boundaries, but they do correspond to county boundaries in most cases. Thus it was possible to merge these district numbers with demographic data from the Census Bureau.
One thing that makes the LCMS useful for this kind of study is that it is one of the whitest denominations -- about 95 percent non-Hispanic white. So it made sense to look at white birthrates in each of these districts.
The figure below shows this relationship. We see clearly that those districts with comparatively high white birthrates were also the regions where the LCMS is suffering less overall decline.
The usual caveats about ecological inference apply, but when we combine this with the other evidence we have seen on this subject, we can make a pretty compelling argument that the health of a Christian denomination is largely predicated on the average size of its families.