The story is relatively clear here. Polling averages become slightly more predictive throughout the fall, but until Thanksgiving they typically had a value of around 0.6 or less on a scale of zero to one (where zero means the polls predict absolutely nothing and one means the polls can be used to perfectly predict the final outcome). A value of 0.6 isn’t very good, but neither is it meaningless. For instance, around Thanksgiving of 2011 the RCP average for the Iowa Republican caucuses had Michele Bachmann, Rick Santorum, Rick Perry and Jon Huntsman at the back of the pack and Newt Gingrich, Mitt Romney, Herman Cain and Ron Paul at the front. Cain and Gingrich would crater and Santorum would surge before the January voting, but the rest of the candidates stayed pretty close to their previous rankings. So the polls at this point in 2011 weren’t perfect predictors, but they were far from useless.
A couple weeks after Thanksgiving, the surveys’ predictive power began to increase bit by bit. That doesn’t mean these primaries weren’t chaotic – a number of candidates saw short-term surges – but that, on average, as voters tuned in more and candidates competed for their support, the polls were better able to discern what the final result would look like. By the time the primary contest rolled around, voters had a pretty good idea of what they were going to do, and the polls reflected that.
This isn’t to say that Thanksgiving is some magical date after which voters decide to pay attention to primaries and that polls suddenly become better predictors. Iowa and New Hampshire are about a month later this cycle than they were in 2008 and 2012, so voters might not start to tune in until late December or early January this time. But our data provide us with a good rule of thumb – the polls will start becoming better predictors soon, so start paying attention to them now and really focus in on them as the actual contests get closer.