Attn:"Poll Watchers", interesting article on "Margin of Error"

[maine_raptor]

From the Wasington Monthly

<snip>

An opinion poll released yesterday found Mr. Kerry had the support of 49 per cent of voters, compared with 47 per cent for Mr. Bush, a statistical tie....

The Globe and Mail reported this as a "statistical tie" because Kerry's 2% lead is within the poll's margin of error (MOE) of 3%. This in turn is based on the theory that (a) statistical results are credible only if they are at least 95% certain to be accurate, and (b) any lead less than the MOE is less than 95% certain.

There are two problems with this: first, 95% is not some kind of magic cutoff point, and second, the idea that the MOE represents 95% certainty is wrong anyway. 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. <end snip>


Here's the link:

http://www.washingtonmonthly.com/

Something to remember when "handicapping the horse race", enjoy!