http://www.pewresearch.org/fact-tank/2018/02/15/voter-files-study-qa/

Since the rise of modern survey research three-quarters of a century ago, much of what we know about voter attitudes has been based on interviews with random samples of voters, sometimes combined with tallies of actual votes and the characteristics of voters in particular locations. But relatively new technologies and public policy changes have given pollsters, academics and other researchers – not to mention candidates and political professionals – a potentially powerful new tool for probing the electorate: digital databases that claim to cover most of the U.S. adult population.

Despite their widespread use, these national databases (commonly called “voter files”) are little known by the general public and haven’t received much scholarly attention. Pew Research Center’s Ruth Igielnik, a research associate, and Senior Survey Advisor Scott Keeter recently released an extensive study of the completeness and accuracy of commercially available voter files, which they assessed by matching participants from the Ce