My Nationaljournal.com column, on the challenge posed to pollsters by third party candidates like Ralph Nader and Bob Barr, is now online.
The topic is timely since yesterday we also put up a new chart showing the results of national poll questions that include Nader and Barr as choices. One issue posed in the column was which form of the vote choice question is a better measure of support for the third party candidates: Those that include Nader and Barr as choices along with McCain and Obama or those that offer only the two major candidates (but typically record the preferences of those who volunteer a choice for another candidate).
I explore the reasons for skepticism toward the four-way vote question in the column. We have historical evidence that summer polls are poor predictors of November support for third party candidates (short version: the summer polls overstate their ultimate support). A more difficult question is which type of question -- the two-way or four-way choice -- provides a better measure of true preferences right now?
My hunch is that reality of Nader and Barr's current support lies somewhere in between the numbers that volunteer their support on questions offering only Obama and McCain as choices and those that offer all four. I believe that many voters are telling pollsters they support Barr or Nader now, especially when offered the four-way choice, because they are not entirely sold on Obama or McCain and would rather grab for the "independent"** as a way to give the interviewer a satisfactory answer (rather than trying to think through their final decision right there on the phone -- a tendency survey methodologists sometimes call "satisficing").
This mushiness of support is something that David Moore touched on in his post here yesterday. You can also see evidence of the conflict in the fascinating cluster analysis of last month's USA Today/Gallup poll written up today.
**Or Libertarian or Green Party candidate. Incidentally, at least one commenter has wondered whether pollsters typically identify the candidate party on these vote questions, and the answer is almost always yes. You can usually get the actual language of the poll questions by clicking through the links in the tables below our charts or in the always invaluable, PollingReport.