With all of the 2010 gubernatorial races completed, polling firms can now be graded on the accuracy of their polls. Among the 5 most popular polling firms, Left and Right News ranks SurveyUSA as having the most accurate polls, followed by PPP, CNN, Rasmussen, and Quinnipiac. These rankings consider the following statistics of each polling firm: the number of gubernatorial polls a firm released, the number of these polls in separate races, the average error of each firm, and last but not least is the “close-knit factor.” The close-knit factor measures the percentage of the total number of gubernatorial polls a firm released and the number of those polls within 2% of the actual outcome. The chart below lists these statistics for these 5 polling firms for all polls released between October 4th and November 1st.
Survey USA had the smallest difference between its polls and the actual outcome of each race with an average error of 3.2%. Additionally, the close-knit factor for SurveyUSA was also high at 29.4% (among the 17 gubernatorial polls released from SurveyUSA, 5 polls were within 2% of the actual outcome, so the close-knit factor is 29.4%). PPP had a slightly higher close-knit factor with 29.6%, but at the same time PPP also had a much greater average error than SurveyUSA. The comparison of these 2 factors ultimately shows SurveyUSA as more accurate. Though, at the same time, the higher number of separate races that PPP surveyed is also quite respectable and makes PPP a close second to SurveyUSA in overall quality.
Lastly, even though Quinnipiac has the 2nd best average error among these 5 polling firms, Quinnipiac only surveyed 5 separate races. With such a low volume of separate races surveyed, one would expect each poll to be quite accurate, yet this isn’t necessarily the case. The opposite is true for CNN – they polled most states only once, yet 33% of their polls were within 2% of the actual outcome.