Our Confirmation Bias and an Embarrassing Blooper

The three hosts of Anabaptist Perspectives recently released an episode responding to various claims that the world is either getting better or getting worse. We showed a chart from a “Christian optimist” which claimed that 1 in 3 people in the world were Christians in 2010 but that only 1 in 27 were Christians in 1900 and that only 1 in 69 were Christians in 1500. We did not endorse the data, but we did, unfortunately treat it as generally plausible.

One of our friends left the following comment on the episode:

“I really enjoyed the discussion and some of the sentiments really resonated with me! Sadly, it appears to me that the chart mentioned from the Rival Nations article, indicating the rise of the church, is not even close to factual. Not sure where he got his data, but as far as I can tell the percentage of the world that claims to be Christian has stayed at about 1/3 for the last century or more. Even by 1500 it was approaching that number. Total numbers of professing Christians have risen dramatically but percentages have not. If someone has a source for his data I’d love to see it. As far as I can tell he did not have a source for that chart in the article.”

This comment appears to be much closer to reality than the chart we put on screen. Are we just gullible? How badly shall we beat ourselves up?

Our episode under critique

The Rival Nations article that we uncritically accepted

Historical estimates of world population on Census.gov

Blogpost by Pew Research Center about the growth of the church through the 20th century

“Finishing the Task” by Winter and Koch that attempts to identify “Practicing Christians”