Apologies for missing this, but on Monday Patrick Murray, founding director of the Monmouth University Polling Institute, posted a terrific primer on this Tuesday's New Jersey primary. His post includes an intriguing description of their methodology and how they "modeled" turnout that may have lessons for the polls out now on next week's Virginia primary:
The Monmouth University/Gannett New Jersey Poll released two weeks ago showed Christie with an 18 point lead - 50% to 32% for Lonegan. For the record, that poll was conducted using a listed sample of registered Republican voters in the state who were known to have voted in recent primaries. It was further screened 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 on June 2 (give or take 10,000).
Variations in turnout tend to have more impact on primary results than they do on general elections. In general elections, the preferences of non-voters tend to line up fairly well with those who actually go out to the polls on election day. However, for primary elections, particularly with an ideologically-fractured GOP electorate, a factor of just a few thousand voters simply deciding whether or not to show up can swing a close race.
It doesn't look like we have a particularly tight race in this case, although that 18 point poll gap may have narrowed since our last sounding on May 20. I did re-examine our data using alternative turnout estimates. If the GOP primary turnout model is set to well above 430,000 - i.e. a 40-year record turnout for a non-presidential race - the Christie margin in our poll grows to 23 points. Alternatively, if the turnout model is pushed down to about 200,000 - i.e. a typical U.S. Senate race - the gap shrinks to 13 points. That's a swing of 10 points based on turnout alone!
I asked Murray if he would provide us with some post-primary thoughts via a "guest pollster" post, and if all goes well, we should have that posted for you tomorrow. But consider his observations about turnout in New Jersey in the context of the polls released in the last week or two in Virginia:
- The two pollsters that have shown Terry McAulliffe doing best -- SurveyUSA and Research2000 -- have used random digit dial (RDD) samples that cannot use the sort of actual vote history information available for individual respondents on list samples.
- The two pollsters that have sampled using registered voters lists -- Public Policy Polling (PPP) and Moran's pollster, Greenberg-Quinlan-Rosner (GQR) -- have consistently shown McAuliffe running 7 to 10 percentage points lower than the polls using RDD samples. I reported details of the PPP sampling method here. I assume that GQR uses lists in this race because their first release says they identified likely voters using both "vote history in Virginia and self-reported likelihood to vote in the upcoming gubernatorial primary" (emphasis added). Again, vote history is only available with a voter list.
[Note: If you click on any data point in our Virginia chart, embedded below, you can connect-the-dots for surveys from individual pollsters and see how each compares to the overall trend]
- On their last two polls, PPP provides crosstabulations that compares two groups: (1) households with vote history in either of the very low turnout primaries in 2005 or 2006 with (2) households where voters participated in only the much higher turnout 2008 presidential primary. Both polls show Deeds doing better (by 8-10 points) in the lower turnout households. McAulliffe scored 9 points lower in the low turnout households two weeks ago, but just two points lower earlier this week.
- SurveyUSA's summary of their latest survey out today includes these findings that suggest a similar correlation: McAuliffe does best among the subgroups with the historically lowest levels of turnout:
McAuliffe's constituents are Independent and young. In SurveyUSA's turnout model, 20% of likely Primary voters are Independent. If this group votes in smaller numbers, McAuliffe's support is overstated here. In SurveyUSA's turnout model, 19% of likely voters are age 18 to 34. If this group votes in smaller numbers, McAuliffe's support is overstated here.
Combine these findings with the considerable self-reported uncertainty -- half (52%) of SurveyUSA's respondents and 44% of the voters on the last PPP survey say could still change their minds -- and we get a race where the final result may look very different from whatever the final round of polls "predict." Hang on to your hats.
PS: Several big unknowns remain in this race, but one big one is now a bit clearer. Creigh Deed's campaign just sent out a release announcing that they will begin airing a television advertisement touting his recent Washington Post endorsement "on broadcast and cable stations in Northern Virginia." Note, however, that the release provides no details about how much time Deeds is buying on the very expensive DC broadcast stations (that also reach into Virginia, Maryland and DC). If they are committing to a decent sized broadcast buy in the DC market, it's a major gamble. If any of our readers catches this new ad on Washington DC broadcast television, please email me or leave a comment below (or email me).
[Prior association disclosed: David Petts, currently the pollster for the Deeds campaign, was my business partner though 2006].