Joshua L. Kalla, a graduate student in the Department of Political Science at UC-Berkeley, and David E. Broockman, an assistant professor at Stanford Graduate School of Business, teamed up to conduct the very first meta-analysis of studies examining the effects of campaign contact and advertising on voter choice. They uncovered forty studies estimating the effect of “campaign advertising and outreach through the mail, phone calls, canvassing, TV, online ads, or literature drops on voters’ candidate choices.”

When pooled together, these studies showed almost no effect of campaigning on altering a voter’s choice in a general election. (Below: A summary of the effect sizes from some of the studies analyzed. Notice that they’re all over the place.)