A large independent voter turnout is unlikely to bring Gomez a victory over Markey

Some recent news coverage on the topic of the Massachusetts Senate special election seems to imply that a large turnout of independent voters and a low turnout for Democrats would lead to a Gabriel Gomez victory on June 25. A detailed look at the party ID breakdown from all of the Markey/Gomez polls shows that given the candidates' current levels of support, even an unprecedented turnout of independent voters at the expense of Democrats would not lead to a Gomez win.

This table shows the party ID breakdown for all of the public polls that have been conducted for the race between Ed Markey and Gabriel Gomez to represent Massachusetts in the U.S. Senate. While there is similarity across the polls, we get a more statistically relevant result by averaging the polls together. Both of the candidates achieves roughly the same percentage of support from his own party—Markey with 83% of Democrats and Gomez with 84% of Republicans—while Gomez holds a significant 16 point advantage over Markey with independent voters, 58% to 42%.

Each one of the polls also provides its own take on the expected party breakdown of the likely voting electorate. The overall estimate of turnout obtained by averaging the party ID numbers of all six polls give us a 40% Democratic, 14% Republican, and 45% Independent electorate. In this scenario, Markey wins by 10 points, 55% to 45%.

But what would the results be if the party ID breakdown of the electorate on June 25 was different? The bottom part of the table shows a variety of scenarios, including an estimated party breakdown of the Coakley/Brown race (based on late polling), and the 2010 State Election and 2012 Presidential elections (based on exit polls). None of those scenarios puts Gomez closer than 7 points to Markey.

We can also consider the most Gomez-favorable of the party ID breakdowns from the six Markey/Gomez polls—35%-13%-52% in the MassINC poll—which still puts Markey up 6 points. The most extreme scenario is the last where I take the original 40%-14%-45% breakdown predicted by the polls and take 10% of the vote away from Democratic voters and put all 10% with the Independents, giving a 30%-14%-55% split. This most extreme and unlikely of the Independent voter expectations still leaves Gomez 2 points behind Markey at 51% to 49%. It seems that Gomez cannot guarantee a win by shifting the electorate from less Democratic to more Independent.

So how did Scott Brown win the 2010 special election with a generic looking turnout of 41% Democrats, 17% Republicans, and 41% Independents?

The final polls before the January 19, 2010 election suggest that Scott Brown was able to win by obtaining the support of 94% of Republicans, by chipping into the Democratic base with the support of 23% of Democrats, and by dominating among Independents with an amazing 36 point advantage among unenrolled voters.

The history from the 2010 Scott Brown win combined with current polling suggests that Gabriel Gomez is unlikely to win the June 25 special election by simply increasing the turnout of independent voters—instead, he would need to fundamentally shift his level of support with the voters of all three groups. Fundamental shifts in the preferences of the voters, while possible given the upcoming debates and likely ad blitz, are becoming less and less likely with only four weeks until the election.

Making sense of the Markey/Gomez poll differences

Differences are probably due to polling method and likely voter screen—averaging gives a better estimate of Markey's actual lead over Gomez

There have been four polls conducted to gauge voter sentiment in the Massachusetts U.S. Senate race between Democratic Congressman Ed Markey and Republican financial executive Gabriel Gomez. While all of the polls agree that Markey leads the race, the surveys vary widely as to the size of the lead, with a 4 point spread in the PPP poll at the lower end and a much larger 14 point lead for Markey in the recent Suffolk poll.

How should we make sense of the variable polling results in order to find the current state of the race? Rather than cherry-picking a favorable poll for either candidate, we can get a more statistically valid estimate by averaging the polls together, giving Markey 46% and Gomez 38%, with an 8 point lead for Markey. The averaging process greatly increases the sample size and can smooth out polling inconsistencies. Interestingly, this four poll average matches the results of the MassINC poll.

What would explain the differences in the polls?

All of the interviews for the four polls of the Massachusetts U.S. Senate special election were conducted in the single week starting Wednesday, May 1 and ending this past Tuesday, May 7. So what explains the different results between the different surveys?

The biggest difference between the first two polls conducted by the Emerson College Polling Society and Public Policy Polling, and last two polls conducted by MassINC Polling and Suffolk University Political Research Center, is the use of automated polling vs. live interviews. Automated polling systems are not allowed to call cell phones, and while pollsters make an attempt to correct for the different demographics for those people who only have cell phones, automation can lead to different polling outcomes. There is also evidence to suggest that non-cell-phone polling underestimates Democratic candidates' chances.

The automated/live distinction cannot be used to explain the difference between the 8 point margin seen by the MassINC and 14 point lead seen by the Suffolk poll, since both surveys used live interviews. While the different results might be because of various methodological difference or sampling error, a strong explanation is the tighter likely voter screen used by the Suffolk poll:

Using a split sample of landline and cell phone numbers, the Suffolk poll used a tight screen to filter out voters who weren't certain to vote or who couldn't name when the special general election would be held.

It is indeed a tight screen when the respondent needs to identify when the election will be held, especially for an off-season special election being held in June. There is evidence from the special primary polling that more engaged voters like these are more likely to support Markey, which may explain some of his larger advantage in the Suffolk poll.

Name recognition

An 8 point Markey lead with 47 days until the election does not, by any means, guarantee a Democratic victory on June 25, rather it can give us an idea the gap that Gomez would need to close. The challenge for both candidates will be to define himself on his own terms before being defined by the opposition. Gomez has a bigger risk/reward possibility with a full 37% of the respondents not having an opinion about him.

As you might expect, Markey has higher favorables and unfavorables as a more mainstream candidate. Strong advantages for Markey are the great organizational capabilities of the Massachusetts Democratic party and policy positions that closely match those of the Massachusetts electorate.

While it is interesting to look at the differences between the four senate polls, we are likely to be better served by averaging the results together, giving a more robust view of the state of race to replace John Kerry. The result shows Congressman Markey in a strong position with 47 days to go.

Survey Details

• Emerson College Polling Society survey
• Public Pollicy Polling survey
• MassINC/WBUR survey
• Suffolk University Political Research Center/WHDH survey

An interactive map of the First Suffolk State Senate election results

You can click on the map below to access an interactive version with precinct-by-precinct results for the Boston part of the First Suffolk State Senate Democratic primary election between Rep. Nick Collins, Maureen Dahill, and the winner, Rep. Linda Dorcena Forry. The results were obtained from The Dorchester Reporter and are not official, but give a good feel for the regional strengths of Collins and Forry.

Polling of Markey/Lynch race converged on actual result

Congressman Ed Markey defeated Congressman Stephen Lynch in the Democratic primary on April 30 by 57% to 43%, a 14 point margin. The final poll conducted by Public Policy Polling showed that same margin, and the normalized numbers for all of the polls converged on a 58% to 42% split in Markey's favor, remarkably close to the actual result.

The table and graph below show all of the public polls of the Markey/Lynch match-up from January through April. The normalized numbers were calculated by allocating the undecided voters to each candidate in the same proportion as the decided voters so they add up to 100%, allowing for direct comparison between the polls and the actual result.

The trends show the race evening out at a 58% to 42% split, almost identical to the 57.4% to 42.6% split of the unofficial numbers reported for Markey and Lynch the night of the election. This is pretty impressive, given the lack of public interest in the race and the resulting difficulty of determining who would turn out to vote in the special primary. Special kudos to Public Policy Polling, which pretty much nailed the final result.