People who tend to be interested in philosophy and are theists probably tend to go into religion rather than philosophy.

That's one hypothesis. An alternative hypothesis would be to suggest that the more educated one becomes in philosophy the less that religion makes sense, and the clearer it becomes that there is no evidence for theism.

(Note, I'm not advocating for either of these hypotheses, but correlation is not causation.)

Your alternative proposition (hypothesis has a different meaning in philosophy than it does in the sciences) is rather confusing from a philosophical perspective. What is 'educated'? Education is a culturally relative idea that is very hard to closely define. Thus, for a religious person being 'educated' may mean something very different from a gypsy who grows up on the streets of Paris who is very 'educated' in the workings of life on the street. Does the 'educated' individual mean some one who can create amazing works of art? Or, does it indicate some one who has memorized and repeats certain culturally important texts and ideas?

There is certainly a cultural side to philosophy in Modern Western society that is largely anti-religious from the very beginning. I started out as your average fervent evangelical Christian, which I am no longer, but it was initially incredibly uncomfortable in a philosophy department to try to hold on to certain belief systems. However, it is not necessarily for the reasons that one would believe. It is a culturally phenomenon. In older generations, it was entirely unacceptable to be religious and be in philosophy. You were naturally routed towards theology by the university staff because the topics of conversation are entirely different; modern philosophy does not concern itself with the question of religion. Yet, the vast majority of older philosophy professors, when being honest, will acknowledge that despite their atheism there are still countless religious systems that have fascinating thinkers and concepts that are both rational and consistent.

It just so happens that in America, Christianity is the de facto symbol for religion and it is both irrational and inconsistent.

I seriously doubt that. Most "professional philosophers" these days are doing analytical philosophy, and it's been at least 500 years since a non-crazy person has been persuaded one way or the other about God by studying logic.

I suppose Georg Cantor might be an exception to this.

Gödel had an unpublished ontological "proof" [1] that's fairly simple to understand. It hinges on two things: 1.) accepting a logical system in which possibly necessary truths are necessary; 2.) accepting his argument that it's possible for god to exist.

But I guess you said non-crazy.

[1] https://en.wikipedia.org/wiki/G%C3%B6dels_ontological_proof

How about Bayes's theorem for proving the existence of God? http://en.wikipedia.org/wiki/Richard_Swinburne

Not knowing which faculties at which institutions this derives from (although, one could probably assume that they're not Theist institutions) that is a plausible explanation.

However, if you change the Population selection to the "No Affiliation" option the numbers are still pretty skewed in the atheist direction.

It's worth noting that philosophy's questions very often treat theistic worldviews with a significant amount of irreverence. A lot of these questions are relatively worthless when you can answer them with, "Whatever God decided on."

Especially those that answered "Other"...

My guess is Wiccan. Philosophers love their witches [1].

[1] http://www.uwo.ca/philosophy/undergraduate/Courses/2000.html...

You expected more theists or atheists?

Indeed, according to a 1998 survey of members of the National Academy of Sciences [1], the group of philosophers had about the same number of atheists, more theists and less agnostics.

1. http://www.stephenjaygould.org/ctrl/news/file002.html