"wizkid12" did include an important caveat, though he was rather late in supplying it:
Third, one could rightly raise the objection that this is not reflective of Democratic and Republican comments on the whole, but only reflects the claims and comments the St Petersburg Times chose to evaluate. This is a valid point, and it makes me wonder how politfact decides which comments to evaluate. But, on the whole, I get the impression that these are statements of some importance to the national discourse insofar as they have been reported in the media. Still, it would be nice if they let us know how they decide which comments to fact-check.You think?
I'll add one more caveat to wizkid's list: Not only does PolitiFact not stick to politically important statements, it also regularly renders bogus judgments.
I can at least partially answer the question as to how PolitiFact chooses its subject matter: It is a combination of editorial judgment and reader requests. So, if liberal bias doesn't skew the choices enough, political activists can drive PolitiFact to the desired subjects via e-mail.
The third caveat wizkid noted should have been sufficient to pre-empt his post. But I suppose the headline was too much to pass up:
Republicans Lie More Than Democrats - a Politifact-Based Analysis
Gotta love it.