Social Science Statistics Blog

Confounding is an obvious problem here. There are many factors that could influence opinions on health care and the Democrats (ideology, economic performance, etc). The authors clearly consider possible problems of confounding:

How do we know that it's the health-reform bill that's to blame for the low poll numbers for Democratic Senate candidates and not just that these are more conservative states?

First, we asked voters how their incumbent senator voted on the health-care bill that passed on Christmas Eve. About two-thirds answered correctly. Even now, long before Senate campaigns have intensified, voters know where the candidates stand on health care. And second, we asked voters about their preference for Democrat versus Republican candidates in a generic House race. As in the Senate, the higher the level of opposition to health reform, the greater the likelihood that the state's voters supported Republicans.

It might be the case that voters are punishing known health care supporters! But, again, I am not sure that these polls show this. The Senate vote was party-line. If someone knew their senator's party, then they could infer their vote without actually knowing it. They could simply know that Democrats are trying to reform health care and their senator is a Democrat. Under this scenario, the actual vote of the senator would make not difference since our hypothetical voter equates Democrats with health care reform.

Put it this way: do you think that House Democrats that voted against the bill are going to have easy reelection campaigns? That seems like the real test of this hypothesis.

A simple gut check would be to run the same analysis with the stimulus instead of health care. I imagine you would get similar results. The point is that the advice from this article for Democrats--withdraw support for health care reform--is not supported by the data.

UPDATE: Brendan Nyhan over at Pollster makes essentially the same argument.