Knowledge-based information acquisition: norms and the functions of consensus information.

Mill's (1872/1973) method of difference prescribes that the lay scientist should use consensus information as a control condition for the person and distinctiveness information as a control condition for the stimulus when analyzing their causal effects on the occurrence of the target event. However, in studies of information acquisition, subjects have shown a consistent preference for distinctiveness information when answering causal questions about the person, and for consensus information when answering causal questions about the stimulus. To explain this discrepancy, we distinguish between the evaluative, contrastive, and corroborative functions of consensus and distinctiveness information. In addition, we suggest that subjects seek consensus information only if it is relevant to the question posed to them, and if they cannot supply it from their own presupposed knowledge of behavioral norms. We report four information acquisition experiments that provide support for our analysis.