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How Not to Interpret Polls

- July 24, 2008

The Washingtonpost.com, Quinnipiac, and the Wall Street Journal have a new poll, which is advertised as showing this: “McCain Makes Significant Gains in Four Key Battleground States.” (Here is virtually the same headline at the Wall Street Journal and Quinnipiac. I would bet both the Washingtonpost.com and the WSJ were basically transcribing Quinnipiac’s press release.) At least one prominent left-wing blog, Talking Points Memo, calls it a “reality check.”

This analysis is wrong. For two reasons:

1) In 2 of these 4 key states, there has been no meaningful change, given the inherent sampling error in polls. In both Michigan and Wisconsin, McCain’s share is unchanged; Obama’s is down 2 points. See here.

2) Repeat after me: ONE POLL DOES NOT MAKE A TREND. Look at Pollster.com’s poll aggregations for another of these four states: Minnesota.

Only in Colorado does this poll’s numbers appear to conform to a trend. See again Pollster.com.

This kind of analysis may generate clicks for the Washingtonpost.com — which, it must be noted, is largely separate from the Washington Post and its polling outfit — and for the WSJ.com, but this analysis is terrible.