25 polling firms have polled one or more of the 8 Presiential Primaries and Caucuses to date in 2008. Here’s how the pollsters stack-up, ranked from smallest average error to largest average error (where smaller error is better, and zero is perfect).
To put the size of Barack Obama’s South Carolina win into perspective:
- Average Pollster Error in South Carolina’s Democratic Primary was 16.6 points.
- Average Pollster Error in New Hampshire Democratic Primary was 9.6 points.
Additional detail, and caveats, on the jump …
Not all 25 pollsters polled on the same contests or on the same number of contests.
Double-click on the following detailed table if you need to enlarge it to read it.
Error is calculated using the “Mosteller 5″ Measure. The Mosteller 5 Measure works this way: If “Pollster A” says Smith beats Jones by 8 points, and Smith in fact beats Jones by 5 points, then Pollster A has an “error” of 3 (8 minus 5). A 3 would be recorded in the table above for that contest. There are limitations to this and all other measures of pollster accuracy.
For a complete discussion of the different ways that election poll accuracy can be measured, including a summary of all 8 known measures, see this paper presented at the 2006 conference of the American Association for Public Opinion Research.
Any errors in this table, or omissions from this table, should be reported to firstname.lastname@example.org.
SurveyUSA will endeavor to update this chart throughout the 2008 election.