Who are the best and worst polling companies

Yesterday, I posted about the Bloomberg Poll showing Obama 13 points ahead of Romney.  I said in that post that this poll is probably an outlier since it differs from a number of other recent polls that show that the race is very close/maybe even.

Some people have asked me about Selzer & Company, the company that conducted the poll for Bloomberg.  I’m not personally familiar with Selzer so I took a look at chart Nate Silver has put together at Five Thirty Eight that rates pollsters.  Selzer comes in sixth out of a very long list of polling organizations so it is pretty good.  That doesn’t mean Selzer can have an occasional outlier but it does mean there is no reason to think Selzer is trying to rig the results.

If you are interested in how other polling organizations are ranked on Silver’s chart check out the chart below and a more complete chart at: http://www.fivethirtyeight.com/search/label/pollster%20ratings  You may want to keep this chart handy as you read the results of various future polls.

The thing to look at is a pollster’s PIE.  PIE is expressed as a positive number and reflects the amount of error that a pollster introduces above and beyond that which is unavoidable due to things like sampling variance. The lower a firm's PIE the better.  

Note: Selzer & Co. gets a PIE of 1.31, sixth from the best.  That's better than NBC/WSJ, AP-Gfk, Mason-Dixon, Pew, and Gallup.