http://talkingpointsmemo.com/livewire/nate-silver-sam-wang-election-forecastsByDYLAN SCOTTPublishedSEPTEMBER 17, 2014, 11:46 AM EDT
Election forecaster Nate Silver did something unusual on Wednesday: He openly criticized another election forecaster's modeling.
The target of his critique was Princeton University's Sam Wang, whose 2014 forecasts have been published by The New Yorker. Silver took the unusual step, he wrote at FiveThirtyEight, because of the disparity between his model and Wang's. Silver's most recent forecast Tuesday gave the Republicans a 53 percent chance of taking over the Senate. Wang's Wednesday forecast shows Democrats with a 70 percent chance of keeping it.
"I don’t like to call out other forecasters by name unless I have something positive to say about them -- and we think most of the other models out there are pretty great," Silver wrote. "But one is in so much perceived disagreement with FiveThirtyEight’s that it requires some attention. That’s the model put together by Sam Wang."
"That model is wrong," Silver said.
Silver took issue with the Wang model's methodology and weighing of polling averages.
"It substantially underestimates the uncertainty associated with polling averages and thereby overestimates the win probabilities for candidates with small leads in the polls," he said. "This is because instead of estimating the uncertainty empirically -- that is, by looking at how accurate polls or polling averages have been in the past -- Wang makes several assumptions about how polls behave that don’t check out against the data."
He cited specific examples like the 2010 Nevada Senate race. Wang's model gave Senate Majority Leader Harry Reid (D-NV) only a 30,000-to-1 chance of keeping his seat against Republican candidate Sharron Angle, Silver said, while FiveThirtyEight by contrast afforded Reid 5-to-1 odds.
Both were wrong, he acknowledged, but "those are very different forecasts."
Wang indirectly responded to Silver's critique in a post of his own on Wednesday, writing that there was a difference between his model's Senate poll snapshot (which gave Democrats an 80 percent on Wednesday) and its forecast which allowed for some uncertainty between now and November (and in turn put the Democratic odds at 70 percent).
Wang did not immediately respond to TPM's request for additional comment.
