Complex sentence: Other sources for such data include exit polls (until recently conducted primarily by the now-defunct Voter News Service) and the U.S. Census; the relative accuracy of these data sources, which frequently disagree, is a matter of considerable debate.
Split into simpler sentences: Other sources for such data include exit polls (until recently conducted primarily by the now-defunct Voter News Service) and the U.S. Census. The relative accuracy of these data sources, which frequently disagree, is a matter of considerable debate.