Under the "conformity" hypothesis, then, if neighbors were like-minded, the recipient's future contributions should go up; if neighbors were mostly of the opposite party, the recipient's future contributions should go down. And that is what happened. In highly polarized areas, for instance, with 75 percent of neighbors supporting one party, same-party supporters contributed 15 percent more, but opposite-party supporters contributed 41 percent less. So, if you're a Democrat in a Democrat area (or a Republican in a Republican area) you would contribute more when feeling observed by neighbors. On the contrary, if you're a Democrat in a Republican area (or a Republican in a Democrat area), you would contribute less when feeling observed by neighbors.
Letters in the "comparison" arm of the study, meanwhile, also provided information about public FEC records, but this time listed a broader array of neighbors. By choosing a random sample of neighbors to list in the letter, the authors created random variation in the information shown to each recipient of the letter. The idea here was to test whether future contributions were influenced, not only by being observed by neighbors, but by observing and reacting to the contributions of neighbors. The expectation: If people you identify with give more, you also should give more. And if they give less, you might feel it's OK to give less.
Once again, the results matched up: For every additional $100 above the party's average contribution given by same-party neighbors, letter recipients' own contributions increased by $13.60. And there was no increase when opposite-party neighbors gave more.
An interesting caveat: In cases where there were higher numbers of same-party neighbors relative to opposite-party neighbors, letter recipients gave less, not more. The authors say this can be interpreted as free-riding behavior; that is, "My friends have it covered."
Prior to this study, political scientists had uncovered evidence on the power of social pressure and social norms for voting turnout. In a famous 2008 study, Professors Alan Gerber, Donald Green and Christopher Larimer sent letters close to Election Day, listing neighbors and previous turnout histories and promising to publicize future voting behavior. As you might expect, voter turnout soared. Unlike other forms of political participation, however, the act of voting doesn't reveal party affiliation. As a result, the social effects on voting turnout are non-partisan. The study by Perez-Truglia and Cruces shows that social pressure can affect political participation in decidedly partisan ways.
In the second study, forthcoming in the Review of Economics and Statistics, Perez-Truglia reinforced his case by showing that people are more politically active when they're in like-minded social environments.
Using data from the Federal Election Commission and the U.S. Postal Service, Perez-Truglia identified 45,108 people who contributed more than $200 to Barack Obama's 2008 campaign and then changed their address either between 2008 and the beginning of the 2012 election cycle, or after the 2012 election had concluded.
Some moved to regions with more Democrats, some to regions with fewer. Perez-Truglia's research shows that after moving to a more Democrat area, the Democrat mover starts making higher contributions. Perez-Truglia uses rich data on the timing of the moves and the contributions to show these are not just correlations, they reflect causal effects of the social environment. He found that increasing the share of Democrats by 1 percent increased contributions to Obama by 0.11 percent. Thus, moving an individual from an area with 45 percent Democrats to an area with 90 percent Democrats increased her contribution by nearly $250. And the longer people spent in their new area, the greater the effect.
These studies use campaign contributions as a natural laboratory to study the effects of peers. However, the authors suggest that the results from campaign contributions probably extend to other forms of political participation in which party support is revealed, such as talking about politics, sharing political news and attending rallies.
One thing these studies don't address is how people are influenced by those who matter to them most. Neighbors in close physical proximity are one thing, but what of the friends, relatives and co-workers who live elsewhere and yet are more active participants in our daily lives? Could those social effects be even greater? The authors suspect that indeed they could.