Perceiving political polarization in the United States: party identity strength and attitude extremity exacerbate the perceived partisan divide.
Westfall J, Van Boven L, Chambers JR, Judd CM. Perceiving political polarization in the United States: party identity strength and attitude extremity exacerbate the perceived partisan divide. Perspect Psychol Sci. 2015 Mar; 10(2):145-58.