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When Diverse Evidence is (and isn't) Inductively Privileged: The Influence of Evidence Presentation on Children's and Adults' Generalization

When Diverse Evidence is (and isn’t) Inductively Privileged: The Influence of Evidence Presentation on Children’s and Adults’ Generalization Chris A. Lawson (lawson2@uwm.edu) Department of Educational Psychology, UW-Milwaukee, 2400 E Hartford Ave Milwaukee, WI 53211 Abstract The ability to determine that diverse samples provide better evidence for generalization than non-diverse samples is an important inductive skill. Adults tend to utilize the diversity principle of induction (DP), but evidence regarding children’s ability to do so is mixed. The two experiments reported here examined whether the method by which evidence is presented would have an influence on children’s tendency to obey the DP. These experiments with undergraduates (N = 66, Mage = 21.12 years) and preschoolers (N = 62, Mage = 5.27 years) revealed that whether sample items were presented sequentially or simultaneously influenced diversity-based reasoning in children, and in some cases, adults. Specifically, sequential presentation facilitated diversity-based reasoning, and simultaneous presentation did not. Together these results indicate that processes elicited during the presentation of evidence have an important influence on how children and adults use evidence to make inductive generalizations. Introduction People utilize a small set of principles to make inductive decisions (Heit, 2000; Osherson, Smith, Wilkie, Lopez, A., & Shafir, 1990). One such principle, the diversity principle (DP), dictates that evidence that covers a greater scope of phenomena provides better support for a conclusion than evidence that covers a narrow scope of phenomena. Consider the following example in which statements above the line are premises in an inductive argument and the statement below the line represents the conclusion: (1) Hippos secrete uric acid crystals Hampsters secrete uric acid crystals All Mammals secrete uric acid crystals (2) Hippos secrete uric acid crystals Rhinos secrete uric acid crystals All Mammals secrete uric acid crystals Undergraduates find the argument presented in (1) to be stronger than the argument in (2) presumably because the premises in the former provide better coverage of the conclusion category (e.g., mammal), and thus better support for generalization, than the premises in the latter (e.g., Osherson et al., 1990). Findings regarding the use of the DP in children are mixed. For example, studies that employed a category-based induction format (in which items took the form of the example outlined above) found that the DP does not emerge until sometime after 7 years of age (Gutheil & Gelman, 1997; Li, Cao, Li, & Deak, 2009; Lopez, Gelman, Gutheil, & Smith, 1992). However, research using other methodologies found that children younger than 5 years of age respect the diversity principle (Heit & Hahn, 2001; Lo, Sides, Rozelle, & Osherson, 2002; Shipley & Shepperson, 2006). For example, after learning about a child who chose to play with a diverse set of balls (e.g., basketball, cricket ball, and tennis ball) and another who chose to play with a non-diverse set of balls (e.g., 3 footballs), 5-year-olds predicted that the child who played with the diverse set of balls would pick a novel ball to play with (e.g., baseball; Heit & Hahn, 2001). One explanation for these mixed findings is that they reflect differences in domain knowledge. For example children might respect the DP in the social domain because of their keen awareness of preferences as a guide for making social inferences (e.g., Woodward & Somerville, 2000). In contrast, failure to use the DP in category-based induction tasks, which typically include animal categories and novel biological properties, might be due to limitations in children’s biological knowledge (e.g., Carey, 1985; cf. Gelman, 2003). An alternative interpretation is that these mixed findings reflect children’s difficulty incorporating certain features of evidence into their inductive decisions. Success on the category-based diversity task requires, at minimum, the ability to analyze each sample, determine the category shared by the evidence and conclusion animals, and evaluate the extent to which one sample provides better “coverage” of the category. Failure to use the DP in these tasks may be due to limitations in younger children’s capacity to process the available input or to engage in, or integrate, all of these different processes (Lopez et al., 1992; see also Gutheil & Gelman, 1997). From this perspective, many have interpreted diversity-based reasoning as a mature inductive skill that undergoes significant developmental change between the ages of 5 to 8 years (Gutheil & Gelman, 1997; Lopez et al., 1992; Rhodes, Gelman, & Brickman, 2008). A slightly different interpretation, and the focus of the current studies, is that young children are able to engage in diversity-based reasoning but that their ability to do so depends on specific task features (e.g., Heit & Hahn, 2001). Thus, rather than positing that the DP develops later in life, the idea is that the capacity to incorporate and effectively use diversity is a feature of early induction, but that it is masked under certain task demands. One reason to favor this interpretation is the substantial database of evidence indicating that well before their preschool years children have spent a large part of their cognitive lives detecting, and learning from, variability within the available evidence