Gerber, Alan S. & Donald P. Green (2000) "The Effect of a Nonpartisan Get-Out-the Vote Drive: An Experimental Study of Leafletting." The Journal of Politics 62(3): 846-857. DOI: 10.1111/0022-3816.00035
A field experiment assessed the effects of a nonpartisan voter mobilization drive. On the weekend before the 1998 general election, voters in the treatment group received an 8" by 11" card on which was printed a nonpartisan encouragement to vote. This treatment had no effect on the turnout rates of registered Republicans and Democrats, but it increased the turnout of those voters unaffiliated with a major party by approximately 7%. We find that the treatment was particularly effective at increasing voting among those unaffiliated voters who voted in 1996.
Link to article here.