From Phys.org:
RAND, in collaboration with political scientists John Sides of George Washington University, Lynn Vavreck of UCLA and Michael Tesler of UC Irvine, surveyed members of the RAND American Life Panel (ALP), made up of several thousand adults recruited using traditional probability methods such as address-based sampling and random-digit dialing. Although respondents complete surveys on the web, respondents need not have internet access when they are initially recruited, reducing a source of bias and making the sample more representative.
 
For the full story, please visit http://phys.org/news/2016-01-survey-voters-difference-candidates-ideology.html.