Academic journal article Psychonomic Bulletin & Review

Relations between Premise Similarity and Inductive Strength

Academic journal article Psychonomic Bulletin & Review

Relations between Premise Similarity and Inductive Strength

Article excerpt

According to the diversity principle, diverse evidence is strong evidence. There has been considerable evidence that people respect this principle in inductive reasoning. However, exceptions may be particularly informative. Medin, Coley, Storms, and Hayes (2003) introduced a relevance theory of inductive reasoning and used this theory to predict exceptions, including the nondiversity-by-property-reinforcement effect. A new experiment in which this phenomenon was investigated is reported here. Subjects made inductive strength judgments and similarity judgments for stimuli from Medin et al. (2003). The inductive strength judgments showed the same pattern as that in Medin et al. (2003); however, the similarity judgments suggested that the pattern should be interpreted as a diversity effect, rather than as a nondiversity effect. It is concluded that the evidence regarding the predicted nondiversity-by-property-reinforcement effect does not give distinctive support for relevance theory, although this theory does address other results.

Why do some observations lead to broad generalizations, whereas other observations do not have as much influence on people's beliefs? One principle for evaluating evidence is the diversity principle, which states that more diverse evidence should lead to stronger inferences than a narrow sample of evidence does. This principle has been influential in the history of science, capturing scientists' preference for testing a theory with a diverse set of experiments, rather than repeatedly conducting the same experiment or close replications (e.g., Salmon, 1984). There has also been a widespread effort by psychologists to document how diversity of evidence affects the way people carry out a variety of cognitive activities. Thus far, sensitivity to diversity has been found in hypothesis testing (Kincannon & Spellman, 2003; López, 1995) and diagnostic reasoning (Kim & Keil, 2003), as well as in children's reasoning about the physical world (Hayes, Goodhew, Heit, & Gillan, 2003). Furthermore, there is well-established evidence from categorization research that more variable observations promote broader or stronger generalizations (e.g., Fried & Holyoak, 1984; Homa & Vosburgh, 1976; Posner & Keele, 1968).

In an influential study, Osherson, Smith, Wilkie, López, and Shafir (1990) documented diversity effects in adults' informal inductive reasoning by using written arguments such as the following:

(1) Hippos require Vitamin K for the liver to function.

Rhinos require Vitamin K for the liver to function.

All mammals require Vitamin K for the liver to function.

(2) Hippos require Vitamin K for the liver to function.

Hamsters require Vitamin K for the liver to function.

All mammals require Vitamin K for the liver to function.

People judged arguments such as (2) to be stronger than arguments such as (1), showing sensitivity to the greater diversity of the premise categories in Argument 2 (hippos and hamsters).

In general, there has been a great deal of evidence of adults, particularly Western college students, following the diversity principle in inductive reasoning (see Heit, 2000, for a review; and see Heit & Hahn, 2001, for a consideration of developmental work). The main exceptions to the diversity effect seem to be due the use of other knowledge, such as expertise, rather than diversity (e.g., Lopez, Atran, Coley, Medin, & Smith, 1997; Proffitt, Coley, & Medin, 2000). So these exceptions do not invalidate the diversity principle so much as show that it can be overridden by other knowledge (Heit, Hahn, & Feeney, 2005). Indeed, the diversity effect is considered one of the touchstone results explained by previous models of inductive reasoning (Heit, 1998; Osherson et al., 1990; Sloman, 1993).

In a recent paper, Medin, Coley, Storms, and Hayes (2003) reported further exceptions to the diversity principle. …

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