Last week on Fox News Sunday, Brit Hume made an interesting point:

(Clinton) closes well, you know. Late deciders tend to break for her. So she's got a chance here. The question is will she carry that over into the way she keeps campaigning and will she carry it over to these debates, which are very widely watched.

I have heard this point before. She probably earned that reputation after New Hampshire. Of course, we have had many contests since the New Hampshire primary. Is she still a good closer?

There are two ways we could answer the question. First, we could look at the polls that precede a given contest to see whether Clinton improves at the end, or does better than the polls predict. Unfortunately, this is only practical for states like New Hampshire. For the rest, we do not have enough polling data. Second, we could use the exit polls, which include information on when voters decide. If we exclude each candidate's home states (expecting voters to think about the race differently in those states) - we have 21 states to examine. This is the approach we shall take.

The exit polls ask voters if they decided the day of the election, three days prior, a week prior, a month prior, or sometime earlier. If Clinton closes well, we should expect her to do better among "day of" deciders, as well as perhaps "three days prior" deciders. However, there is a complication. What about a state like Utah? We might expect Obama to beat her among all voters, regardless of when they decided. After all, he won the state by 18 points. So, she might do better with "day of" deciders than with the whole electorate, but we will not pick up on the improvement if we examine the raw data.

Our response will be to "standardize" the results. That is, we won't just examine how Clinton did with a particular type of voters, we'll examine how she did with those voters relative to the state's electorate. For instance, Clinton won 42% of the vote in Alabama. She won 58% of "day of" deciders. So, she did better with them than with the whole electorate - consistent with the "closing well" theory. We'll capture this by dividing her "day of" share by her total share to get a standardized score of: 58 / 42 = 1.38. Conversely, she won 55% of the vote in Oklahoma, but only won 50% of day of deciders. So, her standardized score is: 50 / 55 = 0.91. This procedures enable us to see that she did close well in Alabama, but not as well in Utah.

This gives us a handy decision rule. A value less than 1.0 indicates that the candidate did worse with a group than with the whole electorate. A value greater than 1.0 indicates an improvement. So, if Clinton "closes well," we should expect values of greater than 1.0 for the late deciders. These scores will help us see how each candidate's voting coalition solidifies over time.

We can also develop a measure that compares the candidates to one another. For instance, we know that Clinton lost by 14 points in Alabama. However, she beat Obama among "day of" deciders by 19 points. This means that Clinton did 33 points better with "day of" deciders than with the whole electorate. This is a kind of "Clinton improvement factor." A positive value indicates that the type of deciders in question prefer Clinton to Obama more than the whole electorate, a negative value indicates that they prefer her less.

This gives us three statistics - Clinton's "standardized" score, Obama's "standardized score," and the so-called "Clinton Improvement Factor." We have all three statistics for each type of voter in each state. We average them by type across states and report the results in the following table:

Clearly, Clinton does better with "day of" deciders than Obama. Her score of 1.05 indicates that her share of the vote among them is usually greater than her share of the vote among whole electorate. Obama's 0.88 score indicates that his share is usually less than his share of the whole electorate. We also see that Clinton does about 8 points better relative to Obama with "day of" deciders than she does with the whole electorate. So, we can conclude that: (a) Clinton does better with "day of" deciders than with the whole electorate; (b) Obama does worse; (c) "day of" deciders favor Clinton over Obama more than the whole electorate.

Now, let's examine voters who decide earlier. Obama's position improves markedly. He does better with "three day" deciders, "week" deciders, and "month" deciders than he does with the whole electorate. Clinton does worse with each of these groups. What is more, the negative "Clinton Improvement Factor" values show that these groups favor Obama over Clinton more than the whole electorate. If we move back in time, we see that the "earlier" voters favor Clinton a little more strongly than the "day of" voters do. This is when most of Clinton's voting bloc forms.

All in all, we see evidence to support Hume's conclusion. Clinton does well with voters who decide early. Obama then does very well, but Clinton slowly closes the margin. This general trend holds up when we divide the states into subsets. If we look only at states Clinton won*, states Obama won*, states before Super Tuesday*, states on Super Tuesday*, and states after Super Tuesday* - we see the same pattern: Clinton does well far from the election; Obama does well about a month before to the day of the election; Clinton closes the gap on Election Day.

What could explain this pattern? Many theories could - one that I am partial to takes into account the pre-campaign knowledge voters have of Clinton and Obama. Namely, most voters know a lot about Hillary Clinton. They do not require a campaign to learn about her. So, voters who are "predisposed" to support Clinton make a decision early on that is not overturned once they learn about Obama, which happens during the course of the campaign. On the other hand, voters who are "predisposed" to Obama generally do not know enough about him to make a decision before the campaign begins in earnest. When it does, they learn that he's the candidate for them. What about voters who decide very late? They probably either have paid so little attention to the campaign that it has had no effect on their thinking, or they have been paying attention but remain genuinely ambivalent. Either way, Clinton does better among them because she is so well known; both go to the candidate they know more about. My sense, then, is that Clinton does not so much "close well" - a phrase which implies that the shift is a consequence of her own efforts - as she benefits from having been a national figure for nearly two decades.

As of now, this is just a theory. The exit polls by themselves cannot tell us whether this theory, or some alternative, is more likely. We'll have to wait for the release of more detailed data that probes voter psychology in some depth, like the National Elections Study. I think this particular theory is consistent with what we know about voter information levels as well as Clinton and Obama's relative positions in the electorate. I also think it does a good job explaining the variation we have seen. But this just makes it reasonable. We'll know for sure when we have more data.

A final observation. This argument places less importance on the effect of political campaigns than what many media pundits would accept. Too bad. Campaigns matter, for sure - but the fact is that many pundits fail to understand how they matter because they misunderstand the voters. They seem to believe that voters pay as much attention as pundits do - and therefore shifts in the horse race polls imply shifts by voters who are paying a lot of attention and changing their opinions. While it is true that some voters behave in this manner - what we might call "schizophrenic Jeffersonianism" - the vast majority does not. Note the large number of voters who claim to decide late in the exit polls cited above. This is inconsistent with the idea most pundits have of the voters. It also implies that their analytical emphases - i.e. parsing the day-to-day nuances of the campaign to distill their impact - are misplaced.

This will become relevant as we move forward. We should expect the media to analyze the early part of the general election campaign just as they analyzed the early part of the primary, which is this incorrect way. Expect them to over-estimate the importance of the day-to-day events, only to forget them a few days after they occur, and above all to over-emphasize the value of the opinion polls conducted months before November. When they do that, we should remember these exit polls. Despite the fact that the primary campaign lasted something like 13 months - most voters claimed to wait until the last month or later to make a choice.

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Endnotes

^[*] States Clinton Wins (9 States)

^[*] States Obama Wins (12 States)

^[*] Pre-Super Tuesday States (4 States)

^[*] Super Tuesday States (13 States)

^[*] Post-Super Tuesday States (4 States)

-Jay Cost