Getting people to vote
Nobel Prize-winning psychologist Daniel Kahneman suggests that just asking people whether they are going to vote is a good way to get them to actually vote.
Those effects would be small at the margin, but there are those effects that are small at the margin that can change election results. You call and ask people ahead of time, "Will you vote?" That's all. "Do you intend to vote?" That increases voting participation substantially, and you can measure it. It's a completely trivial manipulation, but saying 'Yes' to a stranger, "I will vote"...
(via marginal revolution)
Update: Or perhaps not. This paper by Dustin Cho finds that there's no "statistically significant" correlation between intending to or being asked if you're going to vote and actually voting. (thx, max)