No. This is a category error. Confidence intervals apply to things that can be quantified. God (with a capital G) either exists or He does not. There can be

No. This is a category error. Confidence intervals apply to things that can be quantified. God (with a capital G) either exists or He does not. There can be no confidence interval associated with that, only an assessment of belief. A polytheist could have a confidence interval on the number of gods (lower case g) that exist (e.g. "I am 90% sure that the number of gods is between 10 and 20"). But that is not typically what one is referring to when speaking of atheists and agnostics.