January 13, 2008

Likely Voter Screens and the Clinton Surprise in New Hampshire

(Editor's note: Today's Guest Pollster contribution comes from Professors Robert S. Erikson of Columbia University and Christopher Wlezien of Temple University).

Does the world need one more explanation for the historic failure of the polls to predict Hillary Clinton's victory in the New Hampshire primary? We offer another possible account. Ours does not require unusual last-minute voter shifts in preference, voters lying to pollsters, or any disconnect between the campaign story line in the media and voter decision-making voters.

We suggest as the possible culprit the way pollsters' employ their likely voter screens. Pollsters may have been tricked not by voters shifting their candidate preferences but by a rapid shift in enthusiasm by Clinton supporters at the last minute. It may be that significant numbers of Clinton supporters were uninclined to vote at the time when the pollsters were doing their final interviews but then regained their interest just in time to vote. In short, the surge to Clinton could have been simply due to uncounted Clinton supporters who the pollsters dismissed as unlikely voters regaining their interest in voting.

According to most accounts, the late Clinton gains stemmed from sympathy for Hillary after her rough treatment in the media, Hillary's response to the questioning of her likeability in the final debate, and her tears on election eve. But how did this response come about? Was it due to truly undecided voters with their blank slates turning overwhelmingly to Hillary? Exit polls show no evidence of this. And it is unlikely that voters tuning in late would see the flow of the news moving in Hillary's direction. It is the idea that late-deciders could have done so that is so jarring to media watchers.

If late-deciders did not split for Hillary, maybe it was Obama supporters changing their minds? But it is even more implausible that voters who followed the campaign and settled on Obama as their choice would follow the late news and see a reason to vote for Hillary. Once people "make up their minds" in a campaign they rarely change and then only for seemingly good reasons. Did Obama supporters have reason to shift? Would the internal dialog of massive numbers of voters be: "I support Obama because he is such an exciting candidate...No wait, Hillary just shed a tear so I'll vote for her instead"?

Rather than voters deciding late for Hillary or shifting late to Hillary, we posit that her proportion of eligible voters in the New Hampshire primary was fairly steady in the final weeks. What changed was the enthusiasm of her supporters. It may be that Hillary supporters followed the news and became disillusioned by her decline in Iowa, her loss of momentum, and the general negative arc of her campaign. They were watching and they were responding to the media's storyline. Their response was not to shift to another candidate but to become dispirited. If interviewed by pollsters, their lessening enthusiasm placed them disproportionately in the "unlikely voter" column. Then, after the pollsters stopped calling, Hillary's supporters gained the enthusiasm necessary to motivate them to vote. This may be because Hillary showed her more human side late in the campaign or because it was her campaign was on the brink or for other less obvious reasons. The point is that the preferences of these voters were undercounted by pollsters. No unusual number of previously undecided voters or former Obama supporters is necessary to account for her late surge in the polls.**

Is our story true? We know that shifts in net enthusiasm from one candidate's supporters to the other's are more volatile than shifts in net preference. We also know that pollsters can be very sensitive to these shifts in enthusiasm when identifying likely voters. (See our paper from 2004 on "Likely Voters and the Assessment of Campaign Dynamics" in the Public Opinion Quarterly). Was it simply a very late shift in enthusiasm that caused the New Hampshire polls to go wrong?

Pollsters hold in their data banks the evidence that would tell if our conjecture is right or wrong. Our suspicion is that voter preferences among potential Democratic primary voters were more stable over the campaign's final weeks than generally realized. This shifting dynamic evident in the polls, we suggest, was exaggerated by daily shifts in enthusiasm that caused shifts in the composition of who gets counted as "likely voters." If likely voters first shifted against Hillary and then for, the shifting membership of the "unlikely voters" may have "surged" back and forth in the opposite way. It would be interesting to see if this was the case.

**Of course the pattern also could be explained by changes in enthusiasm among Obama supporters that mirrored what we have posited for Clinton supporter, flowing after the big victory in Iowa and then ebbing after the pollsters left the field.

Typos corrected.

-- Guest Pollster

January 13, 2008 in New Hampshire 2008

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