Friday, January 18, 2008
The Nevada caucuses are upon us, but the polling is scant. As the graphs make clear, we have only four polls since New Years, so the trend estimates here should be taken with more than the usual grain of salt. With just 4 polls, the sensitive red estimator is going to try hard to come close to all the polls, making Clinton and Edwards look like they are experiencing huge trends. Obama's four polls are more clustered, so the red trend is a little better behaved, but still tries hard to find a trend when there truly isn't enough data to support one.
Also, there was no Nevada polling between December 3 and this week, so we have NO IDEA what happened during that time. Both trends are fit to all the data (including polls in 2007 not shown in the plots.) So the blue line is the best conservative guess given all the data in 2007 plus the four polls in 2008. The red line sensitive estimator is, in this case, I think hopeless.
If you force me to choose, I'd take blue in this case. With so little data, you want to be conservative. But you can see the poll-to-poll variation is large for Clinton and Edwards. Perhaps a lot has been changing this week, but you can't be sure it isn't just pollster variation.
And one more caution: as a caucus with very low expected turnout, polling Nevada is at least as perilous as Iowa, if not more so.
For the Republicans, we have only three polls taken this week. The only good news here (statistically speaking) is that McCain, Huckabee and Thompson are all tightly clustered without the large variation we saw for the Dems. Romney, on the other hand, shows a big gap between the first poll, completed BEFORE his win in Michigan and the two polls taken since then. Looks like a bump.
The lack of wild variation lets both trends come closer to the polls, but again just three polls is a ridiculously small number to base much on. I'd stay conservative with Blue here.
Ironic that where uncertainty is intrinsically great because of low turnout and the importance of organization that we also have magnified that uncertainty with so few polls. Makes it hard to be an odds-maker in Nevada.