Researchers' subjective judgments may affect the statistical results they obtain. This possibility is particularly stark in Bayesian hypothesis testing: To use this increasingly popular approach, researchers specify the effect size they are expecting (the "prior mean"), which is then incorporated into the final statistical results. Because the prior mean represents an expression of confidence that one is studying a large effect, we reasoned that scientists who are more confident in their research skills may be inclined to select larger prior means. Across two preregistered studies with more than 900 active researchers in psychology, we showed that more self-confident researchers selected larger prior means. We also found suggestive but somewhat inconsistent evidence that men may choose larger prior means than women, due in part to gender differences in researcher self-confidence. Our findings provide the first evidence that researchers' personal characteristics might shape the statistical results they obtain with Bayesian hypothesis testing.
Keywords: Bayesian inference; confidence; gender; hypothesis testing.