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Murray: Estimating Turnout in Primary Polling


Patrick Murray is the founding director of the Monmouth University Polling Institute and maintains a blog known as Real Numbers and Other Musings.

There are a couple of pieces of accepted wisdom when it comes to contested primary elections versus general elections: 1) turnout has a bigger impact on the ultimate margin of victory in primaries and 2) primaries are more difficult to poll (see point #1).

The voters who show up for primaries come disproportionately from either end of the ideological spectrum. Even in states with closed primaries (i.e. one has to pre-register with a party to vote in its primary), there is still a particular art for determining which groups of voters should be included in the likely voter sample.

Voters' likelihood to turnout generally correlates with their ideological inclination. Last year's Democratic presidential nomination provides a good illustration of this. Lower turnout caucus states saw a bigger proportion of higher educated liberal activists participate in the process. These same voters also showed up in the primary states, but they were joined by a good number of less educated, blue-collar Democrats. Result: Obama basically swept the caucus states, while Hillary Clinton held her own in the primaries. Texas, which held both a primary and a caucus that were won by different candidates, is a stark illustration of this turnout effect.

The same is true for Republican primaries. Lower turnout means a larger proportion of the electorate will be staunchly conservative in their views. As turnout increases, it's moderates who are joining the fray, thus diminishing the conservative voting bloc's overall power. And with the GOP being in its present ideologically-splintered state, small changes in turnout can have a real impact in primaries cast as battles between the party's ideological factions.

To some extent, we saw this play out in New Jersey's recent gubernatorial primary where the two leading candidates were seen as representing different wings of the Republican party. Former mayor Steve Lonegan cast himself as the keeper of the conservative flame, while former U.S. Attorney Chris Christie claimed to adhere to core conservative principles (e.g. anti-abortion), but presented himself as a more centrist option. New Jersey's Republican voters agreed - a plurality of 47% described Christie as politically moderate while a majority of 56% tagged Lonegan as a conservative.

The Monmouth University/Gannett New Jersey Poll released a poll nearly two weeks before the June 2 primary showing Christie with an 18 point lead over Lonegan - 50% to 32%. New Jersey has a semi-open primary - meaning both Republicans and "unaffiliated" voters are permitted to vote (although unaffiliateds have their registration changed to Republican if they do vote). So, technically about 3.5 million out of New Jersey's more than 5 million registered voters were eligible to vote in the recent GOP primary. But in the last two contested gubernatorial primaries only between 300,000 and 350,000 voters were actually cast.

So, how do you design a sampling frame for that? First, it's worth noting that state voter statistics show that extremely few unaffiliated voters ever show up for a primary - certainly not enough to impact a poll's estimates. So we are left with about one million registered Republicans, of whom still only one-third will vote. That is, of course, IF turnout is typical (more on that below).

Our poll for this primary used a listed sample of registered Republican voters who were known to have voted in recent primaries. It was further screened and weighted to determine the propensity of voting in this particular election (based on a combination of known past voting frequency and self-professed likelihood to vote this year). In the end, our model assumed a turnout of about 300,000 GOP voters, based on turnout in the past two gubernatorial primaries.

However, turnout in other recent GOP gubernatorial primaries in New Jersey have gone as low as 200,000 - that was in 1997 when incumbent Christie Whitman went unchallenged. Turnout in contested U.S. Senate primaries is also generally around the 200,000 level. On the other hand, turnout has been much higher than 300,000 as well. It even surpassed 400,000 as recently as 1981.

The GOP primary saw higher than average turnout in 1993 - another year when a trio of Republicans were vying to take on an unpopular Democratic incumbent. So, it was fair to speculate that Governor Jon Corzine's weak position in the polls would give GOP voters extra incentive to turn out in the expectation of scoring a rare general election win. On the other hand, perhaps the state's Republicans have become so demoralized by their poor standing nationally and 12-year statewide electoral drought that turnout could be lower than the 300,000 used for our poll estimate.

Because we had information on actual primary voting history for each voter in our sample - i.e. rather than needing to rely on notoriously unreliable self-reports - it was possible to re-model the data from two weeks ago with alternative turnout estimates. If the GOP primary turnout model was set well above 430,000 - a 40-year record turnout for a non-presidential race - the Christie margin in our poll grew to 23 points. Alternatively, if the turnout model was pushed down to about 200,000 - a typical U.S. Senate race level - the gap shrank to 13 points. In other words, adjusting the primary poll's turnout estimate from 5% to 12% of eligible voters could swing the results by 10 points!

Why? The analysis showed that "strong" conservatives comprise about half of New Jersey's 200,000 "core" GOP turnout - and this group was largely for Lonegan. But when we widened the turnout estimate, more and more moderates entered the mix. As a result, Chris Christie gained one point on the margin for approximately every 25,000 extra voters who "turned out."

On primary day, Christie ended up beating Lonegan by a respectable 13 point margin - 55% to 42% - on a 330,000 voter turnout. Based on the model above, if Republicans had been a lot less enthusiastic, Lonegan may have been able to narrow this gap to 8 points. On the other hand, record level turnout would have given Christie a 16 or 17 point win.

 

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