Inductive generalization involves extending knowledge fromsparse samples of evidence to arrive at broad conclusions.Most of the research in this area has focused on generalizationfrom sparse samples of positive evidence (cases known to shareproperties with known cases; e.g., birds have hollow bones).Much less is known about generalization from samples ofnegative evidence (cases known to lack the propertiesattributed to known cases; e.g., bats do not have hollow bones).This paper reports the results from three experiments thatexamined factors that were believed to influence adults’evaluation of negative evidence. Experiment 1 showed thatwhen selecting among samples most useful for teaching abouta particular category, participants (N=36) preferred sampleswith negative evidence rather than those with single, oradditional, positive evidence. Experiment 2 revealed thatparticipants (N=25) preferred samples with negative evidencethat included a closer (rather than more distant) taxonomicmatch with the category in question. Finally, Experiment 3revealed that adults (N=52) only preferred samples thatprovided a close match when evidence was provided by acompetent informant. Overall these results emphasize theimportant role of pragmatic expectations when reasoning aboutsamples that include negative evidence.

A considerable amount of cognition is, in some way, social. Here we consider one example: our reliance upon experts for information about phenomenon within a particular domain. Novices and experts share some knowledge within a domain in question which is crucial for knowing when to seek expert advice and how to evaluate that advice. Just when we decide to relinquish our own knowledge or skill in deference to an expertise remains an important question for cognitive scientists. Here we explored some conditions that might influence when we choose to defer to experts. In two experiments (N=570) we demonstrated that participants have a greater willingness to defer when experts have provide descriptive information (i.e., facts) about their domain of expertise, than when they provide prescriptive advice about what we ought to do with those facts. We interpret these results from the perspective that individuals exercise greater vigilance when given prescriptive advice in the form of normative statements. From this perspective individuals feel threatened, and therefore are less deferential, when experts tell them what to do, rather than share knowledge with them.

Inductive reasoning is constrained by several principles that govern how we choose to generalize evidence to new cases. Here we focus on diversity principle of induction, which describes the tendency to favor inductive arguments that include a diverse sample of evidence over those that include a homogenous sample of evidence. Several studies reveal that adherence to the diversity principle is influenced by a range of conceptual processes, such as an individuals’ prior knowledge or expectations about the categories and properties represented in the evidence. In the two experiments reported here we examined a contextual factor of the available evidence – the spatial separation of evidence exemplars – that we expected would impact how people reason about diverse samples. We found that when the pictures (Experiment 1) or labels (Experiment 2) used to represent evidence exemplars were presented far apart (approximately 10 cm), participants showed a greater willingness to endorse arguments with diverse exemplars than those with homogenous sample, relative to when these exemplars were placed in close proximity (approximately 1 cm apart). We discuss these results as they relate to existing models of induction.

The present study examined the role of negative evidence on children's inductive generalizations. Three-, 4-, and 5-year-olds (N=98) were asked to generalize from samples with negative evidence and samples with positive evidence that were selected either deliberately or incidentally. Children in all three age groups made a higher rate of generalizations from samples that included negative evidence than from samples that included positive evidence, but only when evidence was described as having been selected deliberately by the experimenter. Furthermore, there were developmental differences in the scope of generalizations such that deliberate sampling elicited a higher rate of generalizations among older children compared to younger children. These results are discussed in light of other work on inductive reasoning that emphasizes the role of dyadic factors on generalization, such as the expectation that informants intend to share relevant information.