Peter Curry at Evangelical Textual Criticism has shared a graphic produced by Paul Foster based on his poll of attendees at the 2011 British New Testament Conference on Pauline Authorship. Foster says:

The survey was not rigorously scientific; only those who felt inclined returned their forms. My estimate is that approximately 70 percent of the audience participated. For each of the thirteen Pauline letters and also for Hebrews respondents were asked whether they considered each letter to be written by Paul, or not, or whether they were undecided. There were approximately 109 respondents, although two more cast an opinion only in relation to 2 Thessalonians, and one or two decided not to record their opinions in relation to the Pastoral Epistles. (p. 171)

And here’s the graph: