The Milwaukee Journal-Sentinel has a poll of Wisconsin out this afternoon. The top line has the race going from an Obama 1-point lead two weeks ago to an 8-point lead today. That’s a shift that defies common sense.
However, that doesn’t mean that they did the poll wrong. Let me explain.
A poll of about a 1,200 respondents in its sample will have a margin of error of about 3% at the 90% confidence interval. If the actual race is Obama 45 – Romney 45, and you select a hundred different random samples from the population, you would expect that 90% of those samples to give you a result of somewhere between Romney 42 and Romney 48. The other ten polls will be outliers of more than the margin of error of 3 percentage points.
I don’t see anything necessarily wrong in the demographices of sample polled. Nor did I observe anything done differently from the poll the J-S did two weeks ago. However, with little reason to believe that the race moved 8-points in Barack Obama’s direction, it is likely that either the earlier poll or this one is an outlier. Given where everyone else is showing the state of the race in Wisconsin, it is probably this most recent poll that is the outlier.
But my standard state poll caution applies: Be very wary of media and university polls of states that are not routinely performed time and time again. Polling at the state level can be very screwy and there are a lot of one-off polls performed with shady methodologies.
Finally, there is one odd thing about this poll. It shows a 100% likelihood of voting even as there are 51 respondents who report being unregistered. Now I believe that Wisconsin has same-day registration, so that might explain the unregistered but likely respondents. However, that wouldn’t explain the other issue. See the table below:
Either the J-S includes only those who say that they are absolutely certain to vote plus those who report that they have early voted in their likely voter sample, or some segment of this likely voter sample is lying about their intent to vote. Anyone know?