This is a study of dishonesty more then attendance. You can't go and just ask, "Do you go to church every weekend. People will lie. Also read the table of church growth over the past 40 years on the page you just quoted. Christianity falling is just as much a "Known Truth" as much as above 50% divorce rate of first time marriages.

Care with studies. Most Christians "just know" Christianity is falling away and pay big money to people who predict the death of the faith (George Barna AKA father of Christians divorce rate is the same or higher then non-Christian divorce rate though the one issue is his numbers were all a lie). The truth is that it has grown in mind blowing numbers and really hasn't slowed down except in Mainline denominations and Catholic Churches. The vast majority of stats are if people were honest to the question did they go to church. The surprise is most people are dishonest that they attend church weekly. Case in point East Sunday attendance is huge compared to normal weekly attendance.

I think people are just being blind to the meteoric rise of Christianity in the past 100 years. In 1910 more then half the Christians in the world were European.

Here is a good academic study. http://www.gordonconwell.edu/resources/Center-for-the-Study-...