Pew Research Center. October 28, 2014.
Voters are reporting roughly similar levels of contact from political campaigns and groups as four years ago, with one notable exception. The share of voters who say they have received a phone call about the election has fallen 12 points since mid-October 2010, from 59% to 47%. This decline has been driven by a fall in the percentage saying they have gotten pre-recorded campaign calls, or robo-calls. Other forms of campaign outreach appear to be close to levels measured in 2010. Nearly two-thirds of voters (65%) say they have gotten printed mail from candidates or political groups; 30% have gotten an email. Slightly fewer voters say they have been visited at home by someone than did so four years ago (14% now, 18% then). And the share of voters receiving text messages from candidates or political groups has remained flat (at 4%) since 2010. [Note: contains copyrighted material].
http://www.people-press.org/files/2014/10/10-28-14-Voter-Contact-release.pdf [PDF format, 16 pages].