Articles and Analysis


How Undecideds Split, 1948-2004

Another look at how undecided voters have ultimately voted.  There is much speculation about this, and I've offered a bit of empirical evidence.  Here is a historical look.

The National Election Study (NES) is the leading academic study of electoral behavior, originally developed at the University of Michigan but now managed by a broad board from many universities. 

The NES got it's start in 1948 when, by a lucky break, the Michigan scholars conducted a foreign policy survey in the fall during the campaign. The survey was not directed to the election, but did include a vote choice item. And then Truman won, and the Michigan survey got it right. So they went back and reinterviewed everyone from the pre-election survey to try to throw light on how the vote came to and what it could help explain about the other polls that got it wrong.

In 1952, the Michigan group developed a new, specifically election oriented, survey. Once more they interviewed before the election and then reinterviewed the same respondents after the election.

Landmark books followed, most prominently The American Voter (1960) by Angus Campbell, Philip E. Converse, Warren E. Miller and Donald E. Stokes. (May I add that it was my honor and pleasure to serve as a research assistant to each of Campbell, Converse and Miller during my graduate career, though a good while after The American Voter!)  And for our purposes, a series of National Election Studies was born, which in every presidential election since 1948 has conducted a pre-post survey, allowing us to glimpse how votes shift from Sept-Oct intentions to November action. The NES is now supported by the National Science Foundation as a public resource for the study of elections. (Google for NES for details.)

So, thanks to these pioneers in electoral research, we can see how undecided voters have divided over the years.  The one caveat is that in most years the sample size of the undecided is modest, so the sampling error is large. But the data at least offer some useful lessons.

The break has ranged from 50-50 to a maximum of 23-66 (the rest going to third parties in 2000).  For incumbent parties the median is 42 and for challengers 53. (Means are less different-- 43 for incumbents to 50 for challengers.) 

What is not accounted for here is dropping out. I've not calculated the percent who don't vote, which is sometimes substantial. Here I wanted to focus on those who actually voted and how that split. Voters count more than non-voters in this case.

I think the most important result for this Tuesday is that the last 60 years give little support for a massively lopsided vote among undecided. At most, a 2-1 split is as good as it gets.


Adrian B:

Hi Charles

Don't you mean "a 3-1 split is as good as it gets" (i.e. 23-66 being almost a 3-1 split) - or am I missing something?

It seems to me that the McCain hope of getting all the undecideds to break his way is fanciful. It may have been possible if he had run a far better campaign and if the economy wasn't on the brink of a recession and if GWB wasn't so impossibly unpopular. If anything I think the undecideds are going to favour Obama by a pretty big margin.

When will we know the results of the undecideds from this election?



It looks to me as if there is a preference for the non-incumbent party, at least from 1972 on.



I thought I'd be clever and see how the undecideds are breaking right now, according to the polls. So I compared the Obama, McCain and Other trends from Pollster with the same figures from a week ago. The result: in the states we're watching, the undecideds aren't breaking at all, at least not yet. OK, they've gone to Obama in Arizona, split in North Dakota (with an edge to McCain) and in Montana (with an edge to Obama), and gone to Obama (along with some McCain supporters) in Georgia, and to McCain (along with some Obama supporters) in North Carolina. In every other contested state, the Other column has stayed the same or grown over the last week.

That's not to say the polls have been static; Obama has made gains in Arizona, Arkansas and New Mexico, while McCain has done the same in Pennsylvania, Alaska and West Virginia. But none of those states are in doubt. In the question mark states, the questions about undecided voters remain unanswered (although both Nevada and Ohio show movement Obama-wards).


Chris G:

But there's also little evidence *against* undecideds breaking for McCain. I take it as strong evidence that a 2-1 or 3-1 margin is well within the realm of possibilities.

While even a lopsided margin is unlikely to defeat Obama, its worth considering that expectations are phenomenally high. Say McCain wins undecideds 3-1. That will translate into a roughly 3-pt margin of victory for Obama, vs a 6-pt margin if they break evenly. That difference could be sizable psychologically.




As I noted elsewhere, if you use the least sensitive setting on Pollster's national chart you get what appears to be a consistent margin since about 10/10, with since then undecideds allocating roughly evenly between Obama and McCain.

So I think that is a little hard evidence in favor of the claim the split is unlikely to be terribly lopsided this year.



Here's some half-baked pseudo-historical wishful thinking analysis:

The big breaks seem to go toward:

1) The candidate earlier perceived to be "inexperienced/not qualified": 1960, 1980, 2000.

2) In favor of the candidate portrayed as ideologically outside the "accepted range": 1964, 1972, 1980

3) Candidate tarred with question about "outsider" characteristics: 1960 (Catholic), 1980 (divorced), 1988 (geek and Greek)

4) Against the party holding the White House for 8 (or more) years): 1952, 1960, 1988, 2000.

Those conclusions would all favor an Obama break. Course, the beauty of quasi-historical analogies is that you can also spin another narrative. E.g., voters break for the demonstrably dumber candidate: 1980, 2000.



How do you reconcile this with the November 1 posting, which shows Gore 2 points behind in the last polls but winning by 1/2 point? Yet today's post shows undecideds going to Bush by roughly 3-1 in 2000.
Thank you for your many great postings, even if this one does not help me at least understand what is happening (or might happen, or might have happened in 2000).


Chris G:

What would be useful is some kind of "within-subject" measure of the extent to which these undecideds (who are nonetheless likely to vote) are a stable group, vs. the number reflecting a larger population of wishy-washy voters who randomly flip their preference b/w Obama, McCain and Und day-to-day. I think the more the latter is happening, the stronger an argument can be made that voters will split fairly evenly given how little change there's been in the Obama-McCain margin (which indicates that these voters may be just as likely to flip either direction on Election Day).

But among those who've truly remained undecided, there's very little basis for any prediction of how they'll break. For all we know these voters share some disposition that's difficult to measure and may only make sense after the election.


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