Originally I was going to suggest asking, "what were your religious beliefs before reading the sequences?"-- and then I succumbed to the programmer's urge to solve the general problem.

However, I guess measuring how effective the sequences are at causing people to change their mind is something that a LW survey can't do, anyway (you'd need to also ask people who read the sequences but didn't stick around to accurately answer that).

Mainly I was curious how many deconversions the sequences caused or hastened.