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For each remaining poll, the Obama - Romney score was computed. The arithmetic mean of the other polls' scores was then subtracted from the Rasmussen Obama - Romney value. Ideally, the result should be zero, but statistically that is very unlikely. A positive result means Rasmussen is overestimating Obama's standing and a negative one means he is underestimating it. For example, for the North Carolina poll cited above Rasmussen said Obama was 4 points behind but the average of the other pollsters put Obama 0.2 behind, so Rasmussen gets a bias score of -3.8 here. Averaging all 82 polls, Rasmussen's mean bias is -1.91 points, that is, Rasmussen appears to be making Obama look almost 2 points worse than the other pollsters.
As a simple example, look at the top line in the table below. on Feb. 16 (before Romney even got the nomination), Rasmussen gave Obama a 22% edge in California, but another poll within a week said Obama was 20% ahead. In this case Rasmussen has a positive bias (for Obama). On the line below, Rasmussen's bias is -2%, that is, against Obama.
Note that this does not necessarily mean Rasmussen is wrong and the others are right. It could be that Rasmussen is right and the others are painting too rosy a picture for Obama. There is no way to know now. Below are the scores for the 82 polls. Here are the results in .csv file. If you want all the 82 polls and the surrounding ones that were averaged, here it is.