Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I even say who wrote them. If you have more recent summaries to add to this collection, send them my way I guess. Sorry for the ads; they cover the costs of keeping this online.
Nickerson, David W. 2008. Is Voting Contagious? Evidence from Two Field Experiments. American Political Science Review 102 (February): 49-57.
Nowhere will you find a human relationship associated with more similarities in voting behavior than you will find between a husband and wife. But what causes husbands and wives to embrace similar ideologies, issue positions, and turnout rates? Maybe it's just that we seek out politically similar dating partners. Maybe it's that husbands and wives share the same political experiences over time.
Or maybe--just maybe--voting is "contagious."
The trouble is, it is difficult to prove empirically whether voting is contagious. To do so requires somehow controlling for selection effects and other outside factors. In the article reviewed here, Nickerson reports on an innovative experiment that does just that. Ahead of the September 10th, 2002, Congressional primaries in Denver and Minneapolis, Nickerson sent canvassers door to door to households that had (exactly) two registered voters. At each household, the canvasser gave a brief message to whomever answered the door. Based on random assignment, each household received either a "get out the vote" (GOTV) appeal or a placebo message about the importance of recycling.
There are actually two experiments going on here. The first tests the direct effect of delivering a GOTV appeal to whomever answered the door. Consistent with previous experiments, Nickerson finds that this group voted at a rate 9.8 percentage points higher than the placebo group.
The second experiment is far more interesting. For it, Nickerson looks at turnout rates among those who did not answer the door. Those who did not answer the door at houses receiving the GOTV message voted at a rate 6.0 percentage points higher than those who did not answer the door in the placebo group. This is the contagion effect.
In other words, 61.2% of the treatment effect was passed on from the mobilized voters to their housemates. This is huge. Nickerson points out that this "contagion effect" has a stronger effect on turnout than education, income, or age.
Of course, every study has its shortcomings. Experiments like this are the gold standard for making a causal claim. However, experiments also suffer from external validity problems--that is, this study's conclusions may not apply in every circumstance. Nickerson points out several potential concerns. Among them:
Nickerson's paper uses the best of methods to make a fascinating contribution to the literature. Still, I would ask just a couple more questions.
First, Nickerson does not randomly select which member of each household receives the message; instead, the message goes to whomever answers the door. It seems plausible that the person more likely to answer the door might differ from the person who does not. Might the effect have been (slightly) different if the message were delivered to the second person instead of the first?
Second, what causes this contagion? Nickerson mentions two possible reasons, the lowered costs of voting (sharing a ride to the polls) and the social pressure to conform (see Gerber, Green, and Larimer 2008). My hunch is that it's the latter; it's easy to ignore your civic duty to vote when your spouse also ignores it, but if your spouse bothers to vote, the situation changes. It might be nice to see further research looking specifically at how social pressures and civic duty operate within the family.
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