Nicholas Kristof in the NYtimes writes about "A Confession of Liberal Intolerance"
"A study published in The American Journal of Political Science underscored how powerful political bias can be. In an experiment, Democrats and Republicans were asked to choose a scholarship winner from among (fictitious) finalists, with the experiment tweaked so that applicants sometimes included the president of the Democratic or Republican club, while varying the credentials and race of each. Four-fifths of Democrats and Republicans alike chose a student of their own party to win a scholarship, and discrimination against people of the other party was much greater than discrimination based on race."
The study is "Fear and Loathing across Party Lines: New Evidence on Group Polarization," by Shanto Iyengar from Stanford University and Sean J. Westwood from Princeton University
American Journal of Political Science, Vol. 59, No. 3, July 2015, Pp. 690–707
The abstract reads:
When defined in terms of social identity and affect toward copartisans and opposing partisans, the polarization of the American electorate has dramatically increased. We document the scope and consequences of affective polarization of partisans using implicit, explicit, and behavioral indicators. Our evidence demonstrates that hostile feelings for the opposing party are ingrained or automatic in voters’ minds, and that affective polarization based on party is just as strong as polarization based on race. We further show that party cues exert powerful effects on nonpolitical judgments and behaviors. Partisans discriminate against opposing partisans, doing so to a degree that exceeds discrimination based on race. We note that the willingness of partisans to display open animus for opposing partisans can be attributed to the absence of norms
governing the expression of negative sentiment and that increased partisan affect provides an incentive for elites to engage in confrontation rather than cooperation.