Implicit diagnosticity in an information‐buying task. How do we use the information that we bring with us to a problem?

Past research suggests that people may make use of diagnosticity information when explicit data regarding P(D | H) and P(D | ˜ H) are given to them. However, people fall victim to pseudodiagnosticity biases and ignore P(D | ˜ H) when such data must be actively sought. This series of four experiments utilized judgment problems in which subjects have knowledge of P(D | ˜ H) but must recognize the relevance of that knowledge for the judgment at hand. It was hypothesized that subjects who genuinely understood the role of P(D | ˜ H) in hypothesis testing would respond to this manipulation of implicit diagnosticity by exhibiting greater confidence and lesser information buying when given evidence of relatively high diagnosticity. In the first three studies, subjects attempted to judge the guilt or innocence of suspects in several fictional crimes. In the fourth experiment, subjects attempted to judge the club membership status of students at their own university. Greater amounts of information were bought when the only available information was of low diagnosticity. Subjects also expressed greater confidence in judgments made using highly diagnostic information. However, within the legal scenario, sensitivity to diagnosticity was dependent upon the implication of the cues received. Results are discussed with respect to Bayesian probability, expected value theory, and a confidence criterion model of information purchasing.