As Election Day draws near, people are wondering if the presidential race will tighten. Will the undecideds swing to McCain, or will Obama continue to maintain his 4 to 11 point lead?

Some point to a "Bradley effect" suggesting that voters are hiding their true feelings from pollsters because of Obama's race, while others say the Bradley effect either never existed or no longer exists. People who think there is a Bradley effect believe that the substantial majority of undecideds are likely to vote for McCain, enabling him to close some of the gap.

McCain should win a larger share of undecided voters than Obama, but it has little to do with race.

With Obama outspending McCain by upwards of 4 to 1, getting enormous traction with newspaper editorial boards, generating the enthusiasm to bring out crowds measured in the tens of thousands, and with Palin treated as more of a punch line than a candidate by the press--it seems likely that if voters are not ready to tell a pollster that they are with Obama, they are unlikely to get there.

But the phenomenon of undecided voters' breaking for McCain need not be called the "Bradley effect." Call it the "Bloomberg effect"--where after $100 million of spending, his mayoral challenger was able to capture essentially all of the 10 point undecided vote. Or call it the "Clinton effect"--where almost all the undecided vote swung away from the popular incumbent and went to Bob Dole. Or call it the "Reagan

They all amount to essentially the same pattern. Call it "the Social Effect." Where there is a perception that there is a "socially acceptable" choice, respondents who do not articulate it, are likely not to agree with it. Are they lying? Or just genuinely torn about taking that route or another? I am not going to psychoanalyze what is going on in their heads, but in the end, the pattern tends to be that those undecided voters vote against that "socially acceptable" choice.

In fact, we saw a preview of this during the Democratic primaries this year. Typically, Hillary Clinton won substantial majorities of all late deciders (those who decided in the last three days of the primary)--i.e. Obama tended to lose the "undecided vote."

At the same time, there were examples where Obama outperformed his final poll numbers--even though Clinton was winning the late deciders. What seems to have happened were two effects that had opposite impacts on polling accuracy. It seems they amount to "The Obama Effect:"

1. The "Social Effect" where "undecided" voters were not going to vote for Obama, and
2. Lopsided Enthusiasm, or an Enthusiasm Effect, leading pollsters to underestimate the turnout of Obama supporters--e.g. African Americans, the young, and the more independent voters.

To test this, I correlated the difference between pre-primary poll estimates of Obama and his actual vote against the relative size of African-American share of Democratic primary vote.