Here are some numbers from Enos and Fowler:
The Romney campaign placed 35.8 million phone calls, sent 3.4 million pieces of mail, and knocked on 2.8 million doors in the state of Ohio alone. The voting-eligible population of Ohio was approximately 8.6 million, so this means that the Romney campaign placed 4.2 phone calls, sent 0.4 pieces of mail, and knocked on 0.3 doors per person. These figures are similar for other heavily targeted states. . . . Qualitative reports suggest that the Obama campaign exerted similar mobilization efforts, focusing more on door knocks and less on phone calls. Therefore, we approximate that the average eligible voter in a heavily targeted state received 7-10 phone calls, 1-2 pieces of mail, and 1-2 door knocks from the presidential campaigns. Assuming that our estimated effects are driven solely by ground campaigning, we would conclude that a treatment including approximately 7-10 phone calls, 1-2 pieces of mail, and 1-2 door knocks increases turnout, on average, by 7-8 percentage points. . . .Another calculation yields a similar conclusion. We previously estimated that presidential campaigning mobilized 2.6 million voters who would not have turned out in the absence of campaigning. Our data from the Romney campaign indicates that they attempted 225 million voter contacts. If we assume that the Obama campaign attempted a similar number, then we could say that 550 million voter contacts produced approximately 2.6 million votes. Again, assuming that all of our estimated effects arise through voter contact, we would conclude that the average effect of a single voter contact on turnout was 0.6 percentage points. . . .
Or, to put it another way:
The average cost of generating a single vote is about 87 dollars.
Higher turnout in battleground states
Enos and Fowler form their estimates by comparing voter turnout in battleground and non-battleground states. There is the possibility, though, that turnout would be higher in battleground states anyway, even without the intense efforts to contact voters. Enos and Fowler dismiss that alternative explanation:
We [Enos and Fowler] have also discussed the possibility that residence in a battleground state influences turnout for reasons unrelated to campaigning. On one hand, an individual’s probability of casting a pivotal vote is higher in swing states, which could increase the direct returns to voting and make one more likely to turn out. On the other hand, the probability of casting a pivotal vote is miniscule in both battleground and non-battleground states. . . . Despite the tiny probability of a pivotal vote in a presidential election, there are other reasons to expect higher turnout in battleground states even in the absence of campaigns. A combination of uncertainty and altruism could provide a rational basis for turnout and could explain higher participation in battleground states. Perhaps individuals in battleground states overestimate their probability of casting a pivotal vote, are more interested in the election for psychological reasons, or exert more social pressure on others for reasons independent of the campaign. We must acknowledge these possibilities, but we believe them to be minimal if not negligible for four reasons. (1) Our placebo tests show that battleground voters were no more likely to be interested in politics or express an intention to vote before the presidential campaign began. (2) The most recent evidence on the effects of pivotality, coming from experiments, suggests that considerations of pivotality have minimal effects on turnout. (3) If non-campaign factors explain our results, we would not necessarily expect to see the greatest effects among those individuals who were more likely to have been targeted . . . (4) Similarly, we would also not expect to see our estimated effect of campaigning increase dramatically in recent elections . . . . Presumably, considerations of pivotally and other non-campaign factors were just as prevalent in previous elections, yet we only see these effects emerge in recent elections as campaign behavior has changed significantly.
(To maintain readability I’ve omitted the citations in the above passage; you can find them by following the link at the top of this article.)
The above arguments are reasonable, and I’ll go with Enos and Fowler that most of the differences they see in turnout, comparing swing states and non-swing-states, represent direct effects of campaigns. But not all, I think. It’s my impression that the whole “battleground state” thing has been much more emphasized in recent elections, not just in campaigning but in the news media and thus in the minds of voters. Part of this may be attributed to increased awareness of the predictability of elections (tricking through the news media after decades of research by various people, including Doug Hibbs, Steven Rosenstone, Jim Campbell, Bob Erikson, Gary King, and . . . me!). One piece of evidence of this increased awareness is the change of campaign strategies noted by Enos and Fowler: campaigns as well as the news media have become increasingly statistically savvy and more focused on swing states. So all of this is happening together.
What does this mean for longer-term trends in voter turnout, which was so high among white men in the late 1800s, moderate in the mid-twentieth-century, and then declining through much of the final decades of the last century? Local campaigning used to be a big deal, of course, back in the pre-“bowling alone” eras of closer communities. So this all makes sense, and I think another paper is there to be written (or maybe already has been written), connecting Enos and Fowler’s findings with larger trends in turnout over time and differences between groups.