Re; Reading opinion polls

Eli Stephens elishastephens at hotmail.com
Sun Jul 13 09:59:36 MDT 2003


>From this story: Canadians Vote Bush Least-Liked President
http://www.commondreams.org/headlines03/0712-04.htm

Environics surveyed 2,018 Canadians between June 12 and July 6. A poll of
that size is considered accurate to within 2.2 percentage points, 19 times
out of 20.

My pet peeve: This poll is not "accurate" to 2.2%. What it is, presumably,
is PRECISE to 2.2%. Accuracy and precision are NOT the same. Precision means
you can make the  same measurement repeatedly and get the same answer
(within 2.2% in this case). Accurate means the answer is CORRECT. If you
weigh something with an improperly calibrated scale, you can get the same
wrong answer every time. Likewise, if you poll only certain types of people
(or a variety of other biases), you may well get the same answer, but it
doesn't mean it is ACCURATE. Just precise.

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