The closeness of the Virgina Governor’s race surprised many political observers. To understand why, take a look at this table, which was created from Real Clear Politics’ helpful summary of the eight polls conducted in the week leading up to election day (October 30-November 5). The top line shows the average (not weighted for poll sample size) performance of the three candidates in the eight polls, including the “don’t know” response option. The second line drops the “don’t knows” and reports how much support each candidate had among those poll respondents who expressed a preference. The third line is the actual election day result. McAuliffe is the only one who performed pretty much as expected.

Sarvis’ support was grossly overstated in closing week polls by a factor of about 1.5 to 1. I am comfortable calling this eminently predictable because I predicted it. It’s simply mathematically harder to predict rare events (e.g., third party votes) than common events; even a few days before the election one poll had Sarvis at double the level of support he actually received.

Less predictable and therefore more intriguing is how Cuccinelli outperformed his polls, whether you analyze them in the aggregate as does the table or individually (none of the eight had him as high as his actual total). One could speculate endlessly about why this happened, but I am partial to Chris Matthews‘ view of polling: If pollsters sounded like Archie Bunker instead of staid professionals, there’s a slice of the electorate who would be more forthcoming about their less-than-enchanting political views.

[Cross-posted at The Reality-Based Community]

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Keith Humphreys is a Professor of Psychiatry at Stanford University and served as Senior Policy Advisor in the White House Office of National Drug Control Policy in the Obama Administration. @KeithNHumphreys