You armchair political observers out there trying to handicap the upcoming Senate bout between Sherrod Brown and Josh Mandel are probably getting a little dizzy. Just yesterday we heard reports the race between the deep-pocketed Republican hopeful and sitting Senator was dead even. Now, over the Wheaties today we see another poll puts Brown ahead by double digits. We're talking a game-change gulf in these two results, so what gives?
Well, it's a difference between the polling, a pretty common difference in the polling, as it turns out. Today's data set was courtesy of poll power house Quinnipiac University. As reported in the Plain Dealer, the incumbent leads 46 to 36 percent among 1,246 possible voters. Monday's poll was done by Rassmussen, which put both candidates at 43 percent of 500 voters.
But the difference between the two studies goes beyond the larger net Quinnipiac cast for the sample. Rassmuseen has a history of overshooting the odds of Republican success.
After the 2010 elections, Nate Silver, the stat guru touched by the gods, wrote on his NYTimes blog about the patterns jumping out of Rasmussen's results.
The 105 polls released in Senate and gubernatorial races by Rasmussen Reports and its subsidiary, Pulse Opinion Research, missed the final margin between the candidates by 5.8 points, a considerably higher figure than that achieved by most other pollsters. Some 13 of its polls missed by 10 or more points, including one in the Hawaii Senate race that missed the final margin between the candidates by 40 points, the largest error ever recorded in a general election in FiveThirtyEight’s database, which includes all polls conducted since 1998.
Moreover, Rasmussen’s polls were quite biased, overestimating the standing of the Republican candidate by almost 4 points on average. In just 12 cases, Rasmussen’s polls overestimated the margin for the Democrat by 3 or more points. But it did so for the Republican candidate in 55 cases — that is, in more than half of the polls that it issued.
Just something to keep in mind. As we get closer to November, you're going to be knocked around the head by a lot of data. It's important to consider the frame when your looking at the picture — particularly considering one of the candidates in this race has about as close a relationship with accuracy as I do with Sofia Vergara.