Voters in the early primary states are making up their minds, or at least picking a candidate when pollsters call. For all that has been written about how unsettled the races in both parties have been, we are now seeing a clear decline in the rate of "don't know" answers to the vote question. Interestingly, that trend is clear in the earliest primary/caucus states, but only faintly visible if at all for the nation as a whole. This is further evidence that early state voters really do pay more attention and move to a choice sooner than the nation as a whole. Looming election days concentrate the mind apparently.
In both parties, the undecided rate has turned down the most in Iowa, to about 5% or a shade less. This is down from about 14% early in the year for Democrats and over 15% for Republicans. Even as recently as November 1, over 14% of Republicans were unable to give a candidate choice. Democrats were at about 11% undecided at that time. In both parties the undecided rate has fallen rapidly in November and December.
New Hampshire also shows some fast movement to a decision. NH Dems have been steadily decreasing their don't know rate all year from 17% in January, but it still stands around 10% across the most recent polls. NH Republicans were a bit slower to choose until the first of December. Since then we've seen a rapid decline to about 8% now.
And in South Carolina where there are fewer polls and the undecided rate has been all over the place, we are seeing evidence of more decision making since early November. That pattern has held for both parties, with Dems now at about 9% and Reps at around 10%.
Nationally there is no trend at all in Democratic undecided rates, which have held at 10% all year. For Republicans there has been a little movement nationally, down from about 15% to about 11% since late October.
Pollsters allow voters a variety of ways to say they haven't decided, so there are various ways we can measure the crystallization of preferences. One is to just use the percent who say they are "undecided", which is simple enough. But some voters, especially early on, pick options like "someone else" or "won't vote" and pollsters vary in how the report the no-preference alternatives. So I've calculated the percent who fail to choose any of the candidates the poll asks about. This is the blue "no preference" line. As it happens, these alternative measures track together pretty well, and recently any gap between them has largely vanished.
You can also see large differences across pollsters in how large an undecided rate they produce. A few national polls have zero percent undecided, while the highs at the same time are over 25% for Republicans and over 20% for Democrats. This is one of the sources of house effects in surveys.
There is one methodological issue that we can't address with these data. Near the end of the race some pollsters push voters harder to get a response to the vote question. That would, of course, artificially lower the "don't know" rate, and to some extent may be what we are seeing in these data. Such practices are not normally disclosed so there is no way to statistically adjust for them here.
