Even when voters have the same factual information, partisan bias leads to very different conclusions. (blog.politics.ox.ac.uk)
[A] new report from the Brennan Center for Justice at NYU School of Law finds that extreme partisan bias in congressional maps account for at least 16 - 17 Republican seats in the current Congress (politics.stackexchange.com)
One point is that when the survey is paid for by a partisan organization promoting a particular point of view, no matter how reputable the vendor that actually does the work, it still presents the appearance of partisan bias, and that's not without reason. (edsource.org)