Of course, the aggregate numbers are only as good as the sum of the reports of the individual churches. Some of them I wouldn't throw a stick at.Many congregations never take anyone off of their roles unless they get a letter saying someone has left.
Some congregations have figured out that the time to evaluate their roster is before they schedule an important vote. This comes after several congregation passed a first vote to leave the ELCA and then were totally caught off-guard by all the people who showed up to vote "no" at the second vote.
The Catholic Church doesn't take you off the roles even after you've left, unless you do something drastic like deny your own baptism or die, making their growth statistics suspect at best.
"Roman Catholics, the largest U.S. church with a reported 69 million members, start counting baptized infants as members and often don’t remove people until they die. Most membership surveys don’t actually count who’s in the pews on Sunday. To be disenrolled, Catholics must write a bishop to ask that their baptisms be revoked..."
....it is possible, for example, to be born Catholic, married Methodist, die Lutheran and still be listed as a member of the 1 billion-member Roman Catholic Church....
"...The Catholic understanding of membership is that a person becomes a member upon baptism and remains a member for life," Gautier said. "Whether you show up at church or not is not what determines whether you're a member."
-- from the thread When It Comes to Church Membership Numbers, the Devil's in the Details
Catholics are leaving the faith at four times the rate that newcomers are joining. "Religious change is not simply a function of retention; it's a function of recruitment. It's both sides of the ledger," explains the Pew Forum on Religion and Public Life's Greg Smith. "In no other religious groups we looked at did we see this high a ratio people leaving versus joining."See also Roman Catholics total 64 million in U.S. ["counting Catholics is really more art than science"]
.... from the thread Does the American Catholic Church Have a Numbers Problem?