Reflections on the Vermont 2016 Presidential Primary Poll

On February 22, 2016, Vermont Public Radio released the results of a statewide presidential primary and issues poll conducted by us, the Castleton Polling Institute. The poll came out of the field on February 17 in order to weight the data and give VPR reporters time to prepare stories putting the polling results in context, and VPR wanted to use that time to reflect on where Vermonters stood in advance of 2016 Town Meeting Day and a presidential primary that was to feature a US Senator from Vermont in the Democratic primary and a topsy-turvy Republican race.

Since the election, I have taken some time to reflect on the poll and how well it reflected the public’s primary preferences; I’m conducting a review of our polling to assess to what extent we had a clear picture of the Vermont likely voters 12 days prior to the presidential primary and whether or not our likely voter model needs an overhaul.

Voter Turnout

We used the 2008 presidential primaries as a basis for estimating voter turnout in 2016, since 2008 is the most recent election where no incumbent (neither president nor vice-president) was seeking the nomination in either party. In addition, we made a presumption that the Sanders’ campaign had created an excitement among younger voters akin to the 2008 Obama campaign. Our poll reinforced these assumptions, showing a high degree of support for Sanders among younger voters and showing that the percentage of votes cast in the Democratic primary would near (but not reach) the level of 2008. Sixty-six percent of poll respondents said that they would take a Democratic ballot, and 22 percent said that they would take a Republican ballot in the open primary; when we adjust for 11 percent that hadn’t yet decided in which primary they would vote (eliminating the 11 percent “unsure” and distributing that percent proportionately among the Democratic and Republican primaries) we had 75 percent in the Democratic primary and 25 percent in the Republican primary. The adjusted values overestimated the Democratic share of primary voters (69 percent) and underestimated the Republican share (31 percent) by 6 percentage points. It appears, given the volatility and excitement surrounding the Republican nomination race that the “unsure” voters gravitated more strongly to the Republican contest.

The Democratic Primary

In our likely voter estimation, 78 percent of the respondents planning to vote in the Democratic primary favored Sanders, in contrast to 13 percent for Clinton; 9 percent were unsure at the time, which is not an unreasonable stance two weeks prior to a primary election. Adjusting for the fact that voters do not cast “unsure” ballots, distributing the “unsure” voters proportionately results in 86 percent for Sanders and 14 percent for Clinton, estimates that perfectly reflect the actual share of the vote for the Democratic candidates.

Tab1_PrimaryReflection
Table 1. Polling support compared with election results for the 2016 Democratic presidential primary

The Republican Primary

Given the volatility of the Republican race in the 12 days from when the VPR poll came out of the field until Vermonters cast their votes, it is not surprising that the estimates of where voters stood on February 17 did not mirror the final Republican vote tally. Using the same process of adjusting for the “unsure” voters (by distributing their votes among the candidates in proportion to the candidates’ share of the vote without “unsure” voters), our likely voter model had Donald Trump winning the Vermont Republican primary with 38 percent of the vote, nearly 6 percentage points higher than his actual share of the vote.

We estimated that Marco Rubio would place second with 17 percent of the vote (adjusted from 15 percent), and John Kasich would finish third with 16 percent of the vote (adjusted from 14 percent). Instead, Kasich finished with 30 percent of the vote and Rubio with 19 percent

Tab2_PrimaryReflection
Table 2. Polling support compared with election results for the 2016 GOP presidential primary

The difference between where we had Trump and Rubio on February 17th and where they finished on March 1 is affected by a great deal of campaign dynamics, but the estimates were well within our poll’s sampling error for the subset of Republican voters (MoE = +/- 9 percentage points). Kasich’s final vote tally, however, fell outside of the margin of error; his final vote share was nearly 14 percentage points higher than where we had his estimate on February 17.

The differences between estimates made 12 days before the election and the final election tallies in the Vermont Republican contest can be attributed to two major factors:

  1. The breadth of the field changed as candidates dropped out of the race, and
  2. The efforts that the Kasich campaign put into Vermont changed Kasich’s prospects after the poll was out of the field.

By the time Vermonters cast their ballots the field had winnowed down to five active candidates; most of the Vermonters who supported Bush (5 percent), Christie (3 percent) and others (2 percent) sought out other candidates to support. Additionally, the 12 percent “unsure”—which we distributed proportionately to candidates based on their poll support—were not likely to go to the candidates who had suspended their campaigns. It is not inconceivable that some of the Bush and Christie support would go to the remaining governor in the race, John Kasich, but that would not explain all of Kasich’s gains.

Between the conclusion of the poll and election day, Kasich was the only candidate to visit Vermont, not once but twice (February 27th and 29th), including a visit to the more densely Republican Rutland County. Given that Vermont is the size of a small congressional district (the average size being 710,767, about 14% bigger than the population of Vermont), it is possible to make measurable gains in a short time because a candidate can reach a large proportion of the voters without the effort and resources it would take in a larger state.

Campaigns matter, and their activity can move voters. To believe otherwise, we could conduct a poll at the outset of candidate announcements and use those results to predict winners. But to do so would be a ridiculous proposition. In primary elections, voters cannot fall back on the decision shortcut of party preference, so candidates have more room to sway voters. The dynamics of the campaigns make it difficult to mirror election day results days before an election when voters have time to change or make up their minds.

The VPR poll asked respondents if they were likely to change their minds before election day. Overall, a majority (59 percent) said that their mind was made up, but among those planning to vote in the Republican primary, a majority (55 percent) said that they might change their mind, as illustrated in Figure 1. The odds are very high that many did in fact cast their ballot for someone other than the candidate they supported in the poll.

Pres Primary Change Mind
Figure 1. Likelihood of changing one’s mind about which candidate respondents will support, by choice of primary

In general, we believe that the VPR poll and the likely voter model employed did an effective job demonstrating public views at that time; in fact, those results mirrored the final outcome in the Democratic primary, where voters had mostly settled on their choices earlier than in the Republican primary. Differences between poll results and the ultimate election results in the Republican primary are easily attributed to the Kasich campaign efforts and the changing landscape in the Republican race in the aftermath of the South Carolina and Nevada primaries.