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View Diary: WTF CNN? Complete misrepresentation of tonight's Snap Poll (39 comments)

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  •  You do NOT double the margin of error. (2+ / 0-)
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    IreGyre, StrayCat

    Kevin Drum debunked this  years ago:

    A poll's MOE does represent a 95% confidence interval for each individual's percentage, but it doesn't represent a 95% confidence for the difference between the two, and that's what we're really interested in.

    In fact, what we're really interested in is the probability that the difference is greater than zero — in other words, that one candidate is genuinely ahead of the other. But this probability isn't a cutoff, it's a continuum: the bigger the lead, the more likely that someone is ahead and that the result isn't just a polling fluke. So instead of lazily reporting any result within the MOE as a "tie," which is statistically wrong anyway, it would be more informative to just go ahead and tell us how probable it is that a candidate is really ahead. As a service to humanity, here's a table that tells you...

    Follow the link for the rest, but I'll tell you here and now that a lead of 8 points with a MOE of 4.5 is right off his chart, and so it's at around a 95% confidence level that Obama is, in fact, on top.

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