538: Bad Math and the Bradley Effect

[mod mom]

Bad Math and the Bradley Effect
Theorem: The amount of time conservatives spend talking about the Bradley Effect is inversely proportional to the fortunes of their candidate.

Sean Oxendine at The Next Right purports to find evidence of a Bradley Effect in the Democratic primaries, something which I also looked for and did not find. The difference between my study and his is that I include all the states, whereas he excludes those which do not fit his argument.

Oxendine initially posts data from a large group of states, but then excludes those from what he calls the "Old Confederacy". The concept, however, is inconsistently applied. Texas (where Obama underperformed slightly) remains in his dataset. But also, the particular geographics of the Confederacy are not especially relevant electorally. Kentucky (where Obama underperformed) does not meet Oxendine's definition whereas Tennessee (where Obama overperformed) does, although the states are two peas in a pod demographically. Oxendine also excludes Iowa, where Obama significantly overperformed. True, Iowa was a caucus, and there is a reasonable argument for exlcuding it (likewise with Nevada, which he also excludes), but if you're trying to hypothesis-test, you ought to go with the more roubst and inclusive standard if you're hoping to affirm a positive finding.

In the 20 states that he does choose to include, Oxendine reports that Obama underperformed his polling margin by 2 points. This, by the way, is not a statistically signficant figure at either the 90th or the 95th percentile thresholds. Also, I actually get a different result when looking at that same set of states ... using the Pollster.com estimates rather than the RCP averages, as I did for my study, I found that Obama underperformed by 0.2 points rather than 2.0. Whether the Pollster.com or the RCP averages are superior is something we can take up at another time, but Oxendine's is not a very robust fidning if simply switching up the averaging mechanism that we use removes the positive finding entirely.

-snip

So to summarize, Oxendine:

1. Cherry-picks states for his analysis;
2. Touts a finding that is not remotely statistically significant anyway;
3. Touts a finding that would entirely disappear if you used a different poll averaging mechanism, and,
4. Ignores, even if you excuse all of the above and take his claims at face value, the presence of an apparent reverse Bradley Effect that would benefit Obama in three highly electorally significant states.

http://www.fivethirtyeight.com/2008/09/bad-math-and-bradley-effect.html

[FrenchieCat]

1. That is something that the GOP nor polsters are figuring on.....and I think they should!

"the presence of an apparent reverse Bradley Effect that would benefit Obama in three highly electorally significant states."

[mod mom]

2. I heard a report on NPR stating that the Bradley effect had greatly diminished since Bradley's

election, but don't expect to hear the GOP tell you that.