Young Children’s Ability to Integrate Social and Numerical Information: The Origins of Base-rate Neglect by Samantha Gualtieri A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Doctor in Philosophy in Psychology Waterloo, Ontario, Canada, 2019 © Samantha Gualtieri 2019 Examining Committee Membership The following served on the Examining Committee for this thesis. The decision of the Examining Committee is by majority vote. External Examiner Lili Ma Associate Professor Supervisor Stephanie Denison Associate Professor Internal Member Heather Henderson Professor Internal Member Jonathan Fugelsang Professor Internal-external Member John Turri Professor ii Author’s Declaration I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. iii Abstract The seminal work of Kahneman and Tversky (1973) sparked an interest in the biases that govern decision-making, notably due to their findings on adults’ tendency to neglect base-rate information (i.e., prior probability) when it conflicts with social information (e.g., a personality description, or testimony information). Though research over the past 45 years uncovered the conditions that lead to base-rate neglect, very little has investigated the origins of these biases. Young children can use base-rate and social information on their own, but their ability to integrate this information remains poorly understood. Do children show a preference for social information as soon as they are able to use it? Or, does their preference for social information develop over time? The current thesis explores 4- to 6-year-old children’s ability to integrate base-rate and social information, providing insight into the origins of base-rate neglect. In three projects, I assessed young children’s ability to integrate base-rate and social information. A first project investigated children’s use of base-rate information when it conflicted with individuating information (i.e., a personality description). Typically, adults classify an individual by evaluating how well the individuating information matches a stereotypical member of each social group, underusing prior base-rates of the groups in their decision. Using stereotypes familiar to young children, I presented them with an 8:2 base-rate of characters (e.g., 8 nice, 2 mean). One character was randomly selected from the group, with its membership unknown, and children were given a short personality description. By age 6, children performed similarly to adults and over relied on individuating information. Notably, 4- year-olds preferred base-rates more than the older age groups. I further explored these age differences in a second project that manipulated the quality of the base-rate and individuating information given. Six-year-olds’ use of base-rates varied with manipulations depending on the iv strength of the available individuating information. However, 4-year-olds consistently used base- rates across manipulations, even in situations where it would be reasonable to rely on the individuating information. Thus, children seem to initially show a preference for base-rate information and develop a bias toward individuating information by the age of 6, though attempt to reconcile individuating information with base-rates. A third project extended my findings to another type of social information. I presented children with testimony information from a witness that conflicted with base-rates. Rather than integrating information, adults typically use the witness’ accuracy alone, thus neglecting base-rates. Here, 4- and 5-year-olds relied exclusively on an accurate witness, but they integrated information when the witness was less accurate. For young children, testimony from a witness is a strong cue, even stronger than stereotypical information. With findings from the youngest age group tested to date, my dissertation provides evidence that heuristic strategies strengthen with development and vary depending on the type of social information provided. These findings highlight the importance of research on the role of age-related changes in experience and cognitive abilities in information integration strategies. v Acknowledgments Over the last five years, I have received support and encouragement from a number of people. First and foremost, I would like to extend my deepest appreciation to my supervisor, Stephanie Denison, who made this work possible. Without your support, expertise, and advice, I would not have been able to complete this work. Thank you for helping me grow as a researcher and as a person. I am also grateful for my fellow lab mates, past and present, for their support, feedback, and friendship. I am extremely thankful for the support of Liz Attisano, who believed in me more than I ever did. Thanks for always being there for me whenever I needed someone. I am also very grateful to Reem Tawfik, who always encouraged me to advocate for myself. I could not have had a better testing partner. And special thanks to Tiffany Doan, who was there with me throughout this whole journey. I would also like to extend my gratitude to all the research assistants who spent hours recruiting, testing, and coding these data, including, but not limited to: Nicole Asztalos, Bethany Nightingale, Alex Rett, Ashley Blayney-Hoffer, Emily Stonehouse, and Annika Voss. Special thanks to Annika for the extra hours of moral support and writing motivation. I am extremely grateful to the principals, teachers, museum staff, parents, and junior scientists who made this research possible. Finally, I would like to thank my family and friends for supporting me throughout this journey. Special thanks to Bryce for the much-needed emotional support over the last year. I am extremely thankful for the support and encouragement provided by my parents and brothers, who made sure I saw this through to the end. I dedicate this work to my mom, whose love and enthusiasm for children must have sparked something in me. vi Table of Contents Examining Committee Membership ............................................................................................ii Author’s Declaration ................................................................................................................. iii Abstract ..................................................................................................................................... iv Acknowledgments ..................................................................................................................... vi List of Figures ..........................................................................................................................viii List of Tables ............................................................................................................................. ix Chapter 1: Introduction ............................................................................................................... 1 Children’s Use of Statistical and Probabilistic Information ...................................................... 2 Children’s Use of Social Information ...................................................................................... 6 Children’s Ability to Integrate Information ........................................................................... 15 The Current Experiments ...................................................................................................... 18 Chapter 2: The Development of the Representativeness Heuristic in Young Children ............... 20 The Experimental Approach .................................................................................................. 24 Experiment 1......................................................................................................................... 25 Experiment 2......................................................................................................................... 33 General Discussion ............................................................................................................... 43 Chapter 3: Examining Developmental Change in Young Children’s Information Integration .... 48 Experiment 3......................................................................................................................... 53 Experiment 4......................................................................................................................... 59 General Discussion ............................................................................................................... 63 Chapter 4: The Development of a Testimony Bias in Young Children ....................................... 69 Experiment 5......................................................................................................................... 73 Experiment 6......................................................................................................................... 78 General Discussion ............................................................................................................... 86 Chapter 5: General Discussion .................................................................................................. 90 Limitations ...........................................................................................................................