Friday, March 03, 2006

Why Polls Stink

DovBear today posted a recent LATimes/Bloomberg poll that came out, claiming Bush's approval rate was at 38% overall. After the CBS poll earlier this week was found to be skewed, with a too-high sampling of Democrats, I figured I would check the numbers on this one as well. Here's what I figured out, using the first example on Page 6 as an example: (sorry for the formatting)
Q2. Do you approve or disapprove of the way George W. Bush is handling his job as president? (IF APPROVE OR
DISAPPROVE) Do you (approve/disapprove) strongly or do you (approve/disapprove) somewhat?
ALL DEM IND REP LIB MOD CON MEN WOM
Approve (Net) 38 12 43 77 15 35 60 44 32
Approve strongly 19 1 18 51 7 11 39 21 18
Approve somewhat 18 11 25 26 7 24 21 23 14
Disapprove (Net) 58 86 52 19 83 61 38 52 64
Disapprove somewhat 16 16 14 6 17 17 14 14 17
Disapprove strongly 43 70 38 13 66 44 24 38 47
Don’t know 4 2 5 4 2 4 2 4 4
Let's use the first example, net approval of 38%. Assuming an equal proportion of Democrats, Independents, and Republicans, the net approval should be 44%:

Dem: 1/3 (12%) = 4%
Ind: 1/3 (43%) = 14.33%
Rep: 1/3 (77%) = 25.67%

4 + 14.33 + 25.67 = 44

A factor that would work, however, is the following:

Dem: 9/20 (12%) = 5.40%
Ind: 6/20 (43%) = 12.90%
Rep: 5/20 (77%) = 19.75%

5.4 + 12.9 + 19.75 = 38.05

In other words, 45% of the respondents would have to be Democrats, while just 25% were Republicans. Is that a fair poll? Well, yes. It's simply a skewed sample... which is why polls such as this are meaningless.

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