This is a good article from Christian Science Monitor on the recent survey that examined the change in religion that characterizes American spirituality, and one fact of interest is that Catholics retain 68% who are born Catholic, while Protestants retain 80%.
An excerpt.
America is a country on the move in innumerable ways, and religion is no exception. Half of Americans have changed their religious denomination at least once in their lives – many several times – and 28 percent have switched faiths altogether (for example, from Christianity to Judaism). Amid this fluidity, the number of "unaffiliated" adults has grown to 16 percent of the population.
What is behind such extraordinary "churn" in US religious life? As a follow-up to its pathbreaking 2007 survey of the American religious landscape, the Pew Forum on Religion & Public Life released a new survey Monday – "Faith in Flux" – that explores in depth the patterns and reasons for such remarkable change.
Most people who switch their allegiance during their lifetime, the survey finds, leave their childhood faith while they are still young, before the age of 24. Yet the opportunities for attracting them to another religion appear to continue for some time.
The reasons for leaving differ according to the origin and destination of the convert. Roman Catholics, for instance, tend to leave because they don't accept certain church teachings. Those Protestants who switch denominations do so more often in response to life changes such as relocation or marriage, or because of dislikes about institutions or practices.
While 56 percent of US adults remain in their childhood faith, 16 percent left, joined another house of worship at least once, and then returned to their original fold.
Of those raised Protestant, 80 percent remain so, with 52 percent still in their childhood denomination. Twenty-eight percent have moved to another Protestant following, 13 percent are now unaffiliated, 3 percent have become Catholic, and 4 percent joined other faiths.
Of those raised Catholic, 68 percent remain in the faith, 15 percent are now Protestant, 14 percent unaffiliated, and 3 percent in other faiths.