TWO What Does It Mean to be Biased : Motivated Reasoning and Rationality

In this chapter, we provide a historical overview of research on bias in human cognition, ranging from early work in psychology through the detailed, quantitative examinations of belief revision in the 1960s, the Heuristic and Biases program initiated by Kahneman and Tversky, and bias focused research in personality and social psychology. Different notions of “bias” are identified and compared with the notion of bias in statistics, machine learning, and signal detection theory. Comparison with normative models then forms the basis for a critical look at the evidence that people succumb to motivated reasoning aimed at enabling them “to believe what they want to believe.” Psychology of Learning and Motivation, Volume 61   A reader venturing into the psychological literature about human biases soon realizes that the word “bias” means many things to many people. This holds not just for its wider connotations, but even its immediate meaning. Consequently, it seems necessary to start with a survey of the term’s usage. In everyday use, the term “bias” refers to a lack of impartiality or an undue preference: bias is “an inclination or prejudice for or against one person or group, especially in a way considered to be unfair” (Oxford English Dictionary), or “a tendency to believe that some people, ideas, etc., are better than others that usually results in treating some people unfairly” (Merriam Webster). However, even dictionary definitions contain related meanings that lack the negative connotation, with “bias” being described also as “a strong interest in something or ability to do something” (Merriam Webster). Already apparent in these definitions of everyday use are a number of fundamental distinctions: whether bias is a property of beliefs or of decisions, and whether or not it is inherently negative or “wrong.” However, these are not the only dimensions of variation that may structure the debate within the psychological literature. The word “bias” also has sharpened, more technical, meanings—in particular in statistics—that are also sometimes intended in research on bias. Statistical treatments also provide very balanced consideration of when being “biased” might be good, so we will introduce these technical meanings in more detail. We start, however, by an overview of the concept of “bias” within psychological research. 1.1. “Bias” in Psychology Without a more thorough historical analysis than we are willing (or able) to conduct, any overview of the enormous wealth of research on biases and its reception within cognitive and social psychology will necessarily remain subjective and incomplete. Our main goal is to identify broad contrasts and key dimensions of variation thus setting the stage for a more detailed look at a particular class of biases—indicative of “motivated reasoning”— in the second half of this chapter. 1.1.1 Origins Interest in biases within human cognition developed early in psychology. Vaughan’s (1936) book “General Psychology” contains a chapter titled “The Importance of Bias.” On the definition of bias, Vaughan writes: 42 Ulrike Hahn and Adam J.L. Harris