Robopolls, or polls that do not use live interviewers, are “significantly” more favorable to Republicans than Democrats according to polling guru Nate Silver. Robopolls are the most common types of polls because they cost less than polls that require live interviewers.
In New Mexico, the three most recent independent polls in the gubernatorial race have all been so-called “robopolls.” Two of the polls were by Rasmussen and the third was by SurveyUSA, for KOB-TV.
All showed Martinez with a bigger lead on Denish than could be explained by this effect.
Silver explained:
Most of the automated polling firms have a Republican-leaning house effect. For instance, it’s about 2 points for Rasmussen Reports (our estimate for Rasmussen includes polls conducted by its subsidiary, Pulse Opinion Research) and 4 points for SurveyUSA. Another automated polling firm, Public Policy Polling, has almost zero house effect. But some of the smaller robopoll firms, like Magellan and Merriman River Group, also have a Republican-leaning effect.
On average, the robopoll firms have a 2-point Republican-leaning house effect, whereas the live interviewer polls have a 0.7-point Democratic-leaning house effect. The difference between the two, then, is 2.7 points.
The chart below, from Silver, shows the “bias” of each of the automated pollsters.
