11/07/2008 08:36 am ET Updated Dec 06, 2017

Exit Polls and the Undecided Voters

The 2008 exit polls suggest that most the major media pollsters missed an important part of the presidential campaign, as they either failed to measure or mostly ignored the large undecided group of voters just after the major party conventions officially nominated their candidates, and its diminishing size over the next two months.


Unlike in 2004, the 2008 election polls obtained somewhat more detail about how undecided the voters were, and the results support my argument made on several times previously, that many voters mull over their decisions until late in the campaign period.


In the 2008 election, the exit polls show that 4 percent of voters said they made up their minds on Election Day, another 3 percent in the previous three days, and an additional 3 percent within the past week - for a total of 10 percent. That's virtually the same as the 11 percent who said they had made their decision in the past week in 2004 - with 5 percent saying the day of the election, 4 percent the previous three days, and 3 percent the past week.



When Voters Made Their Decisions

2004 and 2008


(Shown on CNN - click column headings at right) Election 2004

CNN.comElection 2008




Day of election



Previous 3 days



Past week



TOTAL (past week)



Last month/In October



In September



Before September (2008)



Before October (2004)



TOTAL before past week




More interesting, the 2008 exit polls suggest that only 60 percent of voters had decided whom to support before September, with about four in ten making up their minds after the major party conventions in August.


While it is certainly difficult for a voter to pinpoint exactly when he or she made a final decision, some pre-election polling data from this year suggests the exit poll results may be pretty good approximations. Of course, most pollsters don't measure the undecided voter directly (which they could do, by asking whom voters intend to choose on Election Day and then asking, "or haven't you made up your mind yet?"), but instead pollsters will often do so indirectly. After the hypothetical, forced choice vote question, for example, the CBS/New York Times poll sometimes asks, "Is your mind made up, or is it still too early to say for sure?" CBS reports that in mid-August 2008, about a third of all registered voters were "uncommitted" - they had either not chosen a candidate initially, or they had mentioned a candidate but then said it was still to early to say for sure if their minds were made up.


A somewhat larger undecided voter group was measured in a 1996 Gallup poll, conducted Sept. 3-5, 1996, which asked voters up front if they had made up their minds - rather than the standard "who would you vote for if the election were held today" question. In that format, 60 percent said they had made up their minds, while 39 percent said they had not, and 1 percent were unsure. Those 1996 figures are similar to what the 2008 exit poll responses suggest as well.


Below are two graphs of voter preferences. The first is based on a reconstruction from the exit poll crosstabs, which show voter preferences including the undecided vote. Of course, such a reconstruction needs to be viewed cautiously. It's difficult for people to remember exactly when they made up their minds, so at best this graph is an approximation of what voter preferences might have looked like for each month.


As you can see, this first graph shows more voters undecided than choosing either of the two major candidates before September, and it shows the decline in the undecided group over time. (Obviously, each time period on the X-axis is not proportional to the number of days in the time period, but the general pattern is obvious.)


The second graph is a reconstruction (averaging) of Gallup's daily tracking poll, using the likely voter results when available, and the registered voter results otherwise. The "last week" results are based on just four days of the week before the election, while the "last 3 days" are based on just those days from the tracking poll. I used this method to approximate the exit poll categories and provide a comparable base of analysis.


In contrast with the first graph, the second graph of the Gallup tracking poll shows no significant change in the undecided voter group from August through Election Day. In fact, Gallup's daily tracking poll, which goes back to March 2008, shows a steady 5 - 6 percent undecided group for the whole seven months - something that not even Gallup researchers can argue (with a straight face) is accurate.


If we believe that the exit polls have any validity in measuring opinion, it's hard to deny the superiority of the first graph in giving poll consumers an accurate picture of the changing electorate during the campaign. The declining size of the undecided vote over the course of the campaign is clearly an important dynamic in the campaign, regardless of whether pollsters will acknowledge it.