Being part of a survey team conducting a survey of active and lapsed Catholics in the early 1980s prepared me to deal with a today's news stories about a Pew study on religious change in the United States. Let me deal with two things I learned back then that make sense now.
Keep in mind that most of these surveys can only measure affiliation through a tangible behavior that is deemed to denote an inner disposition. While scientologists claim to have machines that can measure advancement in their religion, social scientists do not have a soulmeter of any kind.
So, for the most part, the sociology of religion describes behavior of churchgoers, often in rations that are not doctrinally correct. For example, for the study of Catholics we called someone "active" if they went to church on Sunday at least four times a year, not counting major holidays or family occasions.
This is well below the canonical obligation of Sunday Mass, but it is a behavior indication of a certain degree of engagement. Indeed, in most predominantly Catholic countries perhaps a tenth of all Catholics go to Mass on a regular Sunday; in the United States, a survey in the 1990s found attendance as high as 45 to 55%, depending on how you counted it.
OK, my insights now.
First, it is statistically normal for people between the ages of 15 to 30 to "drop out" of the organized religion in which they were raised. This I learned from sociologist Dean Hoge, who led the research teams and wrote the book, long out of print, about the study.
"Normal" to a sociologist only means that a behavior does not deviate significantly from the social average. It doesn't mean it is good or bad. There are many reasons why disaffiliation during adolescence and early adulthood might occur in societies in which this period involves a prolonged crisis.
The various Anabaptist denominations (Amish, Mennonites, Brethren, etc.) developed a detour around this by decreeing that they would not baptize or affiliate infants. Indeed, most Anabaptists don't formally join their churches before marriage.
This leads to the second interesting insight: most people's religious affiliation has very little to do with philosophy or theology.
Most plainly, I learned from interviewing people who had returned to the faith, the pattern was that once they got married, or even more importantly had children, many drifted back to churchgoing. It was almost as if they wanted to give their children something similar to rebel against.
Significantly, also, very, very few people referred to conversion or returning to faith as a process involving study and thought, or the reading of certain works. Most converts wanted to marry a Catholic.
At the time, I found this profoundly disappointing. I had been involved in the conversion of two people who had wrestled with ideas, read and discussed books with me, written lengthy letters with questions and concerns. They were modern St. Augustines, turning from one view to another with thoughtful deliberation.
Even in my questioning of religious faith, I have always felt the theological and philosophical issues were important. The idea of changing to get married or to pass on certain conventions to children seemed and still seems very hollow.
This is why I find the Pew study less than interesting. Yes, 28% of U.S. adults have changed from the church of their fathers (or mothers), more in the younger years. Given the pattern of social research, I doubt they were asked too deeply why.