In terms of polling analysis, I feel as though I have morphed into one of the bi-partisan pundit concern trolls that dominate the big media commentariat whenever Democrats have gained the upper hand in our political discourse (calls for bipartisanship were far less common, of course, during the Republican trifecta). Pretty much no matter what the polling situation is, I stick to my constant refrain "the truth is in between."
Well, I am about to start that refrain again, this time when it comes to the dueling likely voter models floating around the polling universe. Nowhere is the discrepancy between likely voter models more pronounced than in the Gallup tracking poll, which publishes two separate likely voter models every day. One likely voter model, the "traditional" model, includes questions about past voting behavior and assumes 60% turnout of the voting age population. The other, "expanded" model does not ask about past voting behavior, and makes no assumptions about national turnout.
Most Democratic-leaning election websites have decided to use the "expanded" model as the daily Gallup tracking poll number, rather than the "traditional" model. This is the case at TPM, Pollster.com, and fivethirtyeight and, it would appear, among most of the commenters I read on Open Left. I haven't taken sides in this argument before, but I actually think it is a mistake to use only the "expanded" likely voter model and discard the traditional one entirely. As I always say, the truth is in between.
Here are three things that have been true in the past and may or may not be true in 2008:
1. The Presidential race will narrow as election day approaches
2. When we get closer to election day it is better to look at likely voters than to look at registered voters
3. Exit polls are biased in favor of Democrats
Generally speaking, among all the possible predictors of the future, the best predictor is the immediate past. Given the three items listed above, you may have heard 1) that Barack Obama's lead over McCain is likely to narrow because narrowing occurred in 2000 and 2004 and razor thin election day results followed and 2) we should start looking at likely voter polls rather than registered voter polls. Also, since recent exit polling has been overly optimistic for Democrats you might assume that whatever exit poll leaks you read about on Nov. 4 will need to be adjusted downward for Dems.
I propose that past is not always prologue. In particular I think 2008 is very different from 2000 and 2004 and I'll offer my opinions on the three areas after the jump.
