Who's polling The Minnesota Governors race

Only four pollsters; Rasmussen, SurveyUSA, Princeton Survey Research Associates (PSRA) and Humphrey Institute, have polled the Minnesota Governors race this year and with under a month left before the election it's unlikely that many more will jump in. In 2006 these same four pollsters (StarTribune had in-house polling in 2006, now they contract with PSRA) were joined by Mason-Dixon, St. Cloud St. and Polimetrix, so it's possible that one of them or someone else entirely will drop a poll on us but for now we're just going to look at who's been polling it so far.

A few notes on terms and formatting first.

PIE is Pollster Induced Error, a metric developed by Nate Silver, it's a measure of how much error, above average, a pollster contributes based on an analysis of past polls.

Past election results are listed as follows:
Race Polled: Last polling result (Actual results) Margin Difference
The margin difference is the polling margin minus the actual margin.