Gallup’s methods of measuring religious identity have changed over the decades, but one major trend that is clear from Gallup’s and other organizations’ surveys is the increase in the percentage of Americans who do not have a formal religious identity. Some 60 years ago, in 1951, for example, just 1% of Americans in Gallup surveys said they didn’t have a religious identity. At that time, Gallup classified 68% of Americans as identifying with a non-Catholic Christian faith, and 24% who were Catholic.

Separate Gallup questioning earlier this year shows that 92% of Americans say they believe in God. This suggests that the lack of a religious identity is not in and of itself a sign of the total absence of religiosity.