"I'm worried," said the governor, "and I need your advice. In my brief time here in the province, I've already met quite a few people who are undoubtedly insane. I find this troubling, and I think we need to conduct a survey to find out just how many people in the province are suffering from insanity. What do you think?"
"Well, Governor, I don't think that's the right approach," replied Nasruddin. "What makes you suspect there are any sane people here in the province to begin with?"
Inspired by: Mulla's Donkey and Other Friends by Mehdi Nakosteen
Notes: This story is on p. 81 of the book.