The Incumbent Rule

Incumbent Rule Interpreting Polls Legacy blog posts The 2004 Race

October 3, 2004October 1, 2019 Mark Blumenthal44 Comments

In discussing recent poll results, I said last week that I tend to focus most on President Bush’s job rating and percentage of the vote (which tend to track closely with each other), adding, “that both are hovering just at or above 50 suggest an ultimately close contest, with Bush receiving just about the support he needs to win.” Many of you asked me to elaborate, and I had been meaning to write up an explanation of what pollsters often refer to as the “Incumbent Rule,” that explains why the undecided vote often breaks toward challengers in races featuring an incumbent.

Then, just as I started writing this up in earnest, another Democratic pollster named Guy Molyneux, a partner at Peter D. Hart Research Associates, beat me to the punch. His excellent article in the American Prospect, “The Big Five-Oh,” which appeared online on Friday, makes more or less the same argument I had been promising. It is worth reading in full, but let me first give you the gist and offer some additional supporting evidence.

The basic idea is that voters make their decisions differently in races involving an incumbent. When newcomers vie to fill an open office, voters tend to compare and contrast the candidates’ qualifications, issues positions and personal characteristics in a relatively straightforward way. Elections featuring an incumbent, on the other hand, are as Molyneux puts it, “fundamentally a referendum on the incumbent.” Voters will first grapple with the record of the incumbent. Only if they decide to “fire” the incumbent do they begin to evaluate whether the challenger is an acceptable alternative.

Voters typically know incumbents well and have strong opinions about their performance. Challengers are less familiar and invariably fall short on straightforward comparisons of experience and (in the presidential arena) command of foreign policy. Some voters find themselves conflicted — dissatisfied with the incumbent yet also wary of the challenger — and may carry that uncertainty through the final days of the campaign and sometimes right into the voting booth. Among the perpetually conflicted, the attitudes about the incumbent are usually more predictive of these conflicted voters’ final decision than their lingering doubts about the challenger. Thus, in the campaign’s last hours, we tend to see “undecided” voters “break” for the challenger.

That’s the theory. Does it have any empirical support?

· In 1989, Nick Panagakis, president of Market Shares Corporation (the firm that polls for the Chicago Tribune) analyzed results from 155 surveys, most from the late 1980s, all conducted during the last week before an election. In a famous article in The Polling Report, Panagakis found that in 82% of the cases, the undecideds “broke” mostly to the challenger.

His conclusion? “Incumbent races should not be characterized in terms of point spread. [Suppose] a poll shows one candidate leading 50% to 40%, with 10% undecided…Since most of the 10 points in the undecided category are likely to go to the challenger, polls are a lot closer than they look – 50% to 40% is likely to become 52% to 48%, on election day” (emphasis added).

· Just last month, Chris Bowers of MyDD updated Panagakis’ work. Though he found some signs that the incumbent rule might be weakening in state and local races, he found even stronger support for it in presidential elections. In 28 surveys involving presidential elections, 86% showed undecideds breaking mostly to the ~~incumbent~~challenger.

· Finally, Guy Molyneux averaged “the final surveys conducted by the three major networks and their partners” in the last four presidential elections featuring an incumbent (see the table here), and found that,

In three of these the incumbent fell short of or merely matched his final poll number, while exceeding it only once, and then by just a single point (Ronald Reagan). On average, the incumbent comes in half a point below his final poll result…In every case, the challenger(s) — I include Ross Perot in 1992 and 1996 — exceed their final poll result by at least 2 points, and the average gain is 4 points. In 1980, Ronald Reagan received 51 percent, fully 6 percentage points above his final poll results. (emphasis added)

I can confirm Molynuex’s numbers and suggest some additional evidence.

· Clinton’s support in 1996 was even closer to the final result if the average also includes the other final national polls done in 1996: Gallup, Pew, Harris, Hotline/Battleground and Zogby (using their last report that included results for undecided). Clinton’s average on the eight polls was 49% — exactly what he got on Election Day.

· Finally, we can examine Gallup’s near 60-year database of pre-election polls. Unfortunately, on their last poll, Gallup always releases a projection that allocates the undecided to the candidates (and I have not been able to find documentation on how they apportion the undecided). Until 1996, Gallup never reported their final results with undecideds included. Also, prior to the 1980s, the next-to-last Gallup survey each year typically fell as much as a month before the election, when its predictive value was weaker.

	Incumbent	Final Gallup Projection	Actual Result	Differ- ence
1956	Eisenhower	~~60%~~59.5%	57.8%	1.7%
1964	Johnson	64%	61.3%	2.7%
1972	Nixon	62%	61.8%	0.2%
1976	~~Carter~~Ford	49%	48.1%	0.9%
1980	Carter	44%	41.0%	3.0%
1984	Reagan	59%	59.2%	-0.2%
1992	Bush	37%	37.7%	-0.7%
1996	Clinton	52%	49.2%	2.8%
	Average			1.3%
	Source: Gallup

However, the final Gallup projections (sans undecided) show an intriguing pattern: In the presidential elections since 1956 that featured an incumbent, Gallup’s final projection of the incumbent’s vote exceeded the incumbent’s actual vote six of eight times. The only exceptions were Ronald Reagan in 1984 and George H.W. Bush in 1992, and then by only 0.2% and 0.7% respectively. On average, Gallup’s projection of the incumbent’s vote has averaged 1.3 percentage points greater than the actual result. Obviously, without seeing the raw results we can only speculate, but this pattern suggests that Gallup has allocated too many of the undecided over the years to incumbents.

Now, consider the incumbent rule in relation to the recent polls. Bush has received 49-50% of the vote on the RealClearPolitics’ rolling seven-day average since the Republican convention. Similarly, as Molyneux also notes, Bush’s percentage of the vote in key battleground states like Florida, Ohio, Missouri, Iowa, New Hampsire, Nevada and West Virginia now ranges between 48-49% in polls done just before the first debate. In Wisconsin and Colorado, Bush does a bit better (50-51%); in Pennsylvania, Michigan, Minnesota, Maine and Oregon he runs a few points worse (45-47%).

None of this implies that the current standings will determine the final outcome. Where the race ends up a month from now could obviously be different. However, the incumbent rule tells us that, at any given moment, the President’s percentage of the vote relative to 50% is a better indicator of where the race stands than the margin separating Bush and Kerry. It also suggests the appropriate way to read the final polls just before the election (and these are my ranges – others may differ): If the average result of all the final polls (including undecided) puts Bush’s percentage at 50% or higher, the President will likely win. If Bush’s percentage is 48%-49%, the race is headed for a photo finish. At 47% or lower, the President will likely lose (add 1% to these ranges in any state where Ralph Nader is not on the ballot)

The main point: The incumbent’s level of support is more important than the margin.

[Continue with More on the Incumbent Rule]
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Note: Interpretation of political survey data is even more subjective than methodology. Others may disagree, and opposing viewpoints are always welcome in the comment section.

Correction: In the comments, Dwight Meredith correctly noted an apparent error in the values for Eisenhower in the table above, since 60%-57.8% certainly does not equal 1.7%. The correct Gallup estimate for Eisenhower in 1956 was 59.5% (Gallup reported their results to once decimal that year only), so the 1.7% difference was correct. My spreadsheet displayed the rounded value (60%) even though it used 59.5% for the calculation. I’ve corrected the table.

Mark Blumenthal

Mark Blumenthal is political pollster with deep and varied experience across survey research, campaigns, and media. The original "Mystery Pollster" and co-creator of Pollster.com, he explains complex concepts to a multitude of audiences and how data informs politics and decision-making. A researcher and consultant who crafts effective questions and identifies innovative solutions to deliver results. An award winning political journalist who brings insights and crafts compelling narratives from chaotic data.