Positive confirmation bias in the acquisition of information

An experiment is reported which tests for positive confirmation bias in a setting in which individuals choose what information to buy, prior to making a decision. The design - an adaptation of Wason's selection task - reveals the use that subjects make of information after buying it. Strong evidence of positive confirmation bias, in both information acquisition and information use, is found; and this bias is found to be robust to experience. It is suggested that the bias results from a pattern of reasoning which, although producing sub-optimal decisions, is internally coherent and which is self-reinforcing.