Drew Linzer looks at survey bias:
Another Look at Survey Bias: A relatively small number of survey firms have conducted a majority of the state polls… some leaning more pro-Romney, others leaning more pro-Obama…. There have been hundreds of smaller organizations who have released fewer than a half-dozen polls each…. We can’t reliably estimate the house effects for all of these firms individually. However, we can probably safely assume that in aggregate they aren’t all ideologically in sync…. We can then compare the overall error distribution of the smaller firms’ surveys to the error distributions of the larger firms’ surveys…. [I]f the smaller firms’ error distribution matches either the left-leaning or the right-leaning firms’ error distribution, then it’s more likely the case that those firms aren’t significantly biased after all, and it’s the other side’s polls that are missing the mark.
What do we find? This set of kernel density plots (smoothed histograms) shows the distribution of survey errors…. The smaller firms’ error distribution matches that of Quinnipiac, SurveyUSA, YouGov, and PPP. The right-leaning firms – Rasmussen, Gravis Marketing, and ARG – are clearly set apart….
Right now, assuming zero overall bias, Florida is 50-50. The share of Florida polls conducted by Rasmussen, Gravis Marketing, and ARG? 20%. Remove those polls from the dataset, and Obama’s standing improves.