Reply #25: How? Learning more about polls helps explain what's significant

[tameszu]

Among liberal Democrats:

Dean: 28 (down from 35 last month)
Gep: 12
Kerry: 11
Lieb: 11
Clark 10

Overall poll sample size/MoE = 570 Dems

We can't be sure what the size of the "self-described liberal" subsample is, but other poll data suggest that around 20-24% of Americans call themselves liberals, 85%-95% of whom are Dems, and the nation is divided 40-40-20 between Reps/Dems/Indies. This means that if the Rasmussen poll is consistent with those previous findings, it's likely that the "self-described liberal" subsample would be around 50-55% of the Dem sample, or between 230-250 people. The MoE for such a sample size is between 6.5%-7%.

Bottom line: the 1% spread between Kerry, Lieb, and Clark, and the 2% spread between Gep and Clark are statistically meaningless. The three things that this poll confidently tells us are: (1) around the same # of liberal Dems support each of Gep, Kerry, Lieb, and Clark; (2) Dean is by far the most popular 1st place choice among liberals; but (3) significantly fewer liberal Dems support Dean than did 1 month ago.