Motivated scientific reasoning biases, epistemological beliefs, and theory polarization: a two-process approach to adolescent cognition.

Theory-motivated reasoning biases arise when different reasoning skills are invoked to evaluate evidence that is congruent or incongruent with individuals' belief systems. To explore this phenomenon, 66 early and 73 middle adolescents evaluated evidence relevant to their theories of social class or religion. In both conditions, reasoning biases were found, but in-group biases were evident only in the religion condition. In both conditions, higher order scientific reasoning was used to reject theory-incongruent evidence and judgmental heuristics (i.e., cognitive rules of thumb) were used to evaluate theory-congruent evidence. In both conditions, subsequent to the evidence presentation, adolescents' theories became more extreme (i.e., polarized) than at the outset of the experiment. Beliefs regarding the origin, acquisition, and certainty of knowledge, however, appeared to moderate reasoning biases and theory polarization. Age differences emerged on only one index of bias: In the religion condition, middle adolescents were more likely to treat theory-incongruent evidence as implausible. These findings are pertinent to theories of cognitive development, decision making, rationality, and in-group favoritism.