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The election poll and the margin of error

Asked at Two Sigma

A poll reports a candidate at 51%51\% support with a margin of error of ±3%\pm 3\% at the 95% level. A commentator says: "There's a 95% probability the candidate's true support is between 48% and 54%."

Is that correct as a frequentist statement? What would license it? Also, roughly how many respondents give a ±3%\pm 3\% margin?

Show a hint

The true support is a fixed number on election day. And the margin of error is 1.96p(1p)/n1.96\sqrt{p(1-p)/n}.

Your answer

This one is open-ended. Work it through, then check your reasoning against the full solution.

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