On Ignoring Scientific Evidence: The Bumpy Road to Enlightenment

Abstract

It is well accepted that people resist evidence that contradicts their beliefs.Moreover, despite their training, many scientists reject results that are inconsistent with their theories. This phenomenon is discussed in relation to the field of judgment and decision making by describing four case studies. These concern findings that "clinical" judgment is less predictive than actuarial models; simple methods have proven superior to more "theoretically correct" methods in times series forecasting; equal weighting of variables is often more accurate than using differential weights; and decisions can sometimes be improved by discarding relevant information. All findings relate to the apparently difficult-to-accept idea that simple models can predict complex phenomena better than complex ones. It is true that there is a scientific market place for ideas.However, like its economic counterpart, it is subject to inefficiencies (e.g., thinness, asymmetric information, and speculative bubbles). Unfortunately, the market is only "correct" in the long-run. The road to enlightenment is bumpy. 3The concept of mental models is a useful way of thinking about how people make sense of and understand what happens in the world. Thus, in dealing with the physical world, humans share similar mental models concerning the effects of gravity.For example, if you let something slip from your hands, you expect it to fall. Many of our models are the result of our interactions with the world and are largely tacit in nature (Hogarth, 2001). On the other hand, models can also be formalized and Surprising results can have three causes: (1) the method used to obtain the result was flawed (in the example just given, perhaps there is something wrong with your eyesight?); (2) the model really is incorrect (left by themselves, objects do float instead of fall); and (3) there are specific circumstances -perhaps not previously encounteredwhere the model does not apply (perhaps you observed the object while traveling in a space vehicle where gravity has no effect?).Relative to our ability to understand, there is no question that the world is complicated. Thus, the models (and theories) we hold represent the accumulation of both our own experience and that of our ancestors. This knowledge -although 4 imperfect -has taken considerable time to develop and thus, when the predictions of models fail, one can understand why people do not wish to abandon cherished beliefs. seems almost trivial to state that the model should be amended -either rejected as incorrect or specified to be more limited than originally thought. However, the history of science is replete with examples where this does not happen. Indeed, some time ago Kuhn (1962) brilliantly described the difficulty of replacing obsolete scientific paradigms (see also below).The purpose of this chapter is to discuss this phenomenon with respect to the field of judgment and decision making. There are two reasons why this field provides an interesting setting for this issue. First, for scientists ...