Negations and natural sampling in data selection: Ecological versus heuristic explanations of matching bias

Matching bias occurs when people ignore negations when testing a hypothesis-for example, ifA, then not 2-and select possible data types that are named in the hypothesis (i.e., A and 2; Evans & Lynch, 1973). There are two explanations of this bias: the heuristic account and the contrast class account. The latter is part of Oaksford and Chater's (1994) ecological approach to data selection. On this account, a contrast set (i.e., birds that are not ravens) has a higher probability than the original set (i.e., birds that are ravens). This article reports two experiments in which these accounts make divergent predictions. The same materials were used as those in Yama (2001), who found more support for the heuristic approach. Experiment 1 replicated Yama with Western participants. Experiment 2 used a procedure introduced by Oaksford and Wakefield (2003). Rather than present participants with one of each of the four possible data types all at once, 50 were presented one at a time. The proportions of each data type reflected the relevant probabilities. The results supported the ecological approach, showing that people constructed contrast sets that strongly influenced their data selection behavior. The results were not consistent with the heuristic approach.