ABSTRACT Extreme response style (ERS) refers to the tendency to overuse the endpoints of Likert-type scales. This study examined the extent to which ERS is accounted for by measures of personality, specifically, intolerance of ambiguity, simplistic thinking, and decisiveness. One hundred and sixteen pairs of undergraduate students and one of their respective peers completed a battery of questionnaires assessing these personality measures, alongside three measures of extreme responding. Results indicate that peer ratings of intolerance of ambiguity and simplistic thinking interact with the primary participant's time spent on the survey to predict the primary participant's extreme responding. Thus, those who quickly complete surveys and are intolerant of ambiguity or are simplistic thinkers are most likely to exhibit ERS. These results have implications not only for surveys using rating scales, but also illustrate how epistemic personality factors more generally influence the processing of new information.