Overall, the experiment had an effect towards the lower end of what 'get out and vote' campaigns can achieve, says Fowler: door-knocking campaigns can increase voter turnout by about 8%, for example, whereas e-mail campaigns achieve gains of 1% or less, he says. But, Fowler adds, the audience for social networks is large and the study's estimates were conservative, because, for example, many users may have logged onto Facebook too late for the messages to have an effect. Fowler emphasizes that behaviors other than voting won't necessarily be influenced in the same way.
Cameron Marlow, head of Facebook's data-science team and a co-author of the paper, stresses that individuals' identities had been protected in the study. He declined to comment on whether Facebook would deploy any message to help to increase voter turnout at this year's US presidential election.