Comments on: AP Poll Report: A 3.5-Point MOE Means a 14-Point Spread

By: Gordon

Gordon — Thu, 23 Oct 2008 20:38:49 +0000

Media members are so stupid.

Sincerely,
Idiots

By: David Macys

David Macys — Thu, 23 Oct 2008 20:25:44 +0000

Normally I’d nod in agreement with your post on margin of error, but I just read another blogger I normally agree with who in this case agrees with the (gack) AP on this. I don’t know enough to referee this issue, but you might want to check each other’s rationale and conclusions. The other blog is at http://engram-backtalk.blogspot.com/ and the post I’m referring to is today’s. I’m also posting this same comment over there, with your URL, in hopes of a fruitful discussion & resolution. Thanks for the good work you both do, it’s nice to have a few outposts of sanity and reason to rely on for facts.

By: davorider

davorider — Thu, 23 Oct 2008 19:39:30 +0000

Actually, in this case, the AP is right. The MOE is applied to each candidate individually, so of Obama is at 44%, the MOE means he could be as high as 47.5 or as low as 40.5, and McCain, at 43%, can be as high as 46.5 or as low as 39.5. These figures are independent, so if McCain is actually a point higher, it does not mean that Obama is necessarily a point lower.

By: Ben

Ben — Thu, 23 Oct 2008 19:18:31 +0000

From what they had written, here is how I gather how they got the 14-point spread. The 3.5% MOE is for each candidates percentage meaning that McCain could be from 39.5% to 46.5% and Obama could be anywhere from 40.5% to 47.5%.

If McCain was at 46.5% and Obama was at 40.5%, then McCain is 6 points up.
If Obama was at 47.5% and McCain was at 39.5%, then Obama is 8 points up.
Thus, a possible 14 point difference.

I was under the impression that the margin of error is what they were saying. Each candidate could be 3.5% +/- of the reported number. I have seen similar graphs in actual polls that would agree with this.

What you seem to be saying is the that MOE is to be applied to the total difference between the two. Are you sure that is correct?

By: AP Poll Report: A 3.5-Point MOE Means a 14-Point Spread

AP Poll Report: A 3.5-Point MOE Means a 14-Point Spread — Thu, 23 Oct 2008 19:18:24 +0000

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By: mcg

mcg — Thu, 23 Oct 2008 19:18:05 +0000

I don’t think you quite have it right either.

It’s not hard to see how they arrived at those numbers. A 3.5-point error means that Obama could range anywhere between 40.5-47.5, while McCain could range from 39.5-46.5. Taking the extremes on both ends puts Obama between 6 points down and 8 points up.

Now that’s not right; the margin of error on the difference doesn’t double. But is it the same as the MOE? According to this guide, for instance, it’s not: the MOE of the difference is larger than the MOE of the individual numbers. They recommend a multipler of 1.7, which means the difference is about 6 points. Thus Obama could be up by 7 or down by 5.