No sooner had I finished posting my primer on polling than my attention was drawn by Taegan Goddard's Political Wire to a useful Wall Street Journal article on the limitations of political polling. The piece was written by Lauren Ettner and contains some good points about volatility in the electorate before a major election and the impossibility of getting definitive polling results when a significant chunk of the voters hasn't even made up its mind yet. These are useful warnings to keep in mind.
At the end of the article, however, I found a graphic that provides a wonderful teachable moment about what polls tell us and don't tell us. Here's an excerpt from the graphic, showing results from a WSJ/NBC News poll on voter sentiment regarding a Democratic takeover of the U.S. Congress:
What do you think this poll means? While the title says “In 2006, signs point to a Democratic takeover,” this conclusion is not necessarily indicated. One should be much more careful in interpreting what poll respondents mean when they answer a pollster's questions. If you were a rock-ribbed Republican diehard who remained resolute in your support of the Grand Old Party, you could reasonably reply “No effect” to the question “Has what you have seen and heard over the past few weeks made you feel more favorable, less favorable, or had no effect on your feelings about possibly having the Democrats become the majority party in Congress?” After all, you hated the idea before and you still hate the idea right now. No change.
Let me drive the point home by relabeling the poll results (except for Other, which I skipped) in a manner entirely consistent with the responses, but with labels that suggest a dramatically different conclusion from the one in the WSJ title:
Please note that it was obviously necessary to change the data bars to red, reflecting the much more Republican outcome. Now I happen to think that the Wall Street Journal is correct in its conclusion that the electorate is more kindly disposed toward a Democratic Congress and is more likely to vote to elect one. That inference seems reasonable in the light of many other polls and indications. However, it does not ineluctably follow from the responses of the poll's subjects. A sample composed predominantly of determined Republican voters could have produced the very same answers documented in the WSJ graphic.
You've been warned. Don't get complacent. Go out there and vote for all the Democrats you can find.