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The Vagaries of Opinion Polling

October 27th, 2004, 5:30pm by Sam Wang

A brief note on the vagaries of opinion polling. When we read polls we often make the implicit assumption that people report what is really going on inside their heads. However, this is a subjective report. The famous example in these closing days is the “undecided voter.” But are these people undecided in the sense that we mean colloquially? Are they one monolithic category of person?

It’s been pointed out that many undecided voters are unfavorable about the incumbent, and usually break for the challenger. This phenomenon may simply reflect the fact that some people are unable or unwilling to state a set preference. To cite a homely example, you may find yourself unable to articulate what you want for dinner, but you can react immediately to what you don’t want.

Recently Scott Rasmussen reported data that he says supports the notion that late-deciding voters prefer Bush. The survey was done from 136 late-deciding voters, far too few to reach statistical significance. This is a message poll aimed at driving the discussion in his preferred direction. Also, the survey assumes that the voters who decided during the survey period are similar in characteristics to those who wait until the last minute, possibly until they are standing in the voting booth. This is untested.

A parting thought on undecided voters: we are not going to resolve this by further argument! The best we can do is come up with a way to measure what they do, and wait until after the election. I will try to provide this as part of my final Election Night briefing document.

Other examples of respondent inaccuracy are the party-ID question, which can depend on when in the survey it is asked (especially if asked after the presidential preference!) and the question of who people voted for in the last election (on average, people show a tendency to think that they voted for the winner even if they did not).

Finally, once again: the probability map is not the same as the median calculation. This is why they do not match. If you were thinking about writing me to point this out, read this first.

Tags: 2004 Election

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