The SDT model of belief bias: complexity, time, and cognitive ability mediate the effects of believability.

When people evaluate conclusions, they are often influenced by prior beliefs. Prevalent theories claim that belief bias affects the quality of syllogistic reasoning. However, recent work by Dube, Rotello, and Heit (2010) has suggested that belief bias may be a simple response bias. In Experiment 1, receiver operating characteristic analysis revealed that believability affected accuracy for complex but not for simple syllogisms. In Experiment 2, the effect of believability on accuracy disappeared when judgments were made under time pressure and with participants low in cognitive capacity. The observed effects on reasoning accuracy indicate that beliefs influence more than response bias when conditions are conducive to the use of certain reasoning strategies. The findings also underscore the need to consider individual differences in reasoning.