To those in the know: How much of the "mainline Protestant decline/conservative and/or evangelical Protestant increase" can be attributed to differences in birth rates between the two categories of Protestants?
It can't be much. A difference in birth rates could explain a slow drift in membership statistics across many generations, but we're not talking about a subtle change here; we're talking about a nearly complete obliteration of many of the mainline denominations, in the case of the PCUSA losing close to half its members over 30 years.
I'm not sure on the whole what it is, but anecdotally, a lot of the Protestants I know that go to "Evangelical" churches were raised mainline Protestants who went off to college and found their denomination on campus looked nothing like the one they were raised in, so they went elsewhere. A lot of them came from smaller towns with tight-knit communities and a generally more theologically conservative outlook and then come to campus to see something they find unrecognizable. Biblical literalism was replaced by feelings and music by Wesley was replaced by Haugen (or organs by guitars). Either way when people move from place to place the variation they often find within the mainline denominations is sufficiently large that they no longer really see themselves as a part of them anymore.
