From the Gallup Poll.
Results for this Gallup poll are based on telephone interviews conducted as part of Gallup's annual Values and Beliefs surveys each May between 2001 and 2017. Most of these surveys were conducted with random samples of approximately 1,000 national adults, aged 18 and older, living in all 50 U.S. states and the District of Columbia. For results based on the total sample of 17,765 national adults in the aggregated sample, the margin of sampling error is ±2 percentage points at the 95% confidence level. The results based on the aggregated samples of denominational groups vary in sample size from 222 to 1,450, with margins of sampling error between ±3 and ±8 percentage points at the 95% confidence level.
