A couple weeks ago, I worked on calculating survey house effects in approval rating polls on Donald Trump. As more time has passed and the number of polls to examine has increased since then, it’s worth checking in again on what polls are most and least biased on Trump, with other factors held constant. That’s what the below plot shows. (Before that, read the original explanation for how these house effects are calculated.)
Just like three weeks ago, the smallest in-house effect in either direction belong to Gallup. After controlling for polling universe, survey mode, and other variables, the Gallup effect–relative to all other polls–on Trump’s net approval rating is just 0.51 points. Other polls with fairly small house effects are CBS, FOX, YouGov/Economist, and CNN.
On the other end of the spectrum, Quinnipiac has the largest anti-Trump in-house effect–11.2 net points less approval for Trump relative to other polls and all else equal–while Rasmussen has the largest pro-Trump in-house effect at 10.8 points. PPP (D), ICITIZEN, Kaiser FF, Pew, and NBC/SurveyMonkey also have sizable anti-Trump effects, while Suffolk/USA Today, Monmouth University, NBC/WSJ, and Politico/Morning Consult have large pro-Trump effects (greater than five points in either direction). Some of these house effects rely on small amounts of polls to gauge a pollster’s bias, so these results should still be viewed cautiously.