Scientific Truth

In Saturday and elsewhere McEwan has expressed his optimism about the ability of science to unravel the mysteries of the brain and the truth about consciousness. There are several passages in Saturday that deal with general matters of scientific inquiry and method. I was especially struck by this succinct remark.

…statistical probabilities are not the same as truths.

This claim is at the heart of the disenchantment I began to experience with psychology. Psychologists seek to establish very general laws of human thought and action. Yet I never understood how evidence derived by averaging the scores of a group of individuals could serve as the foundation for a science of individual behavior. Laws based on aggregate data tell us very little about specific individuals and serve only to obscure crucial features of human variability and uniqueness. Further, the many exceptions to these laws severely limits their generality. So, it is impossible to say with assurance that they hold for a particular individual at a particular time and place.

This conclusion is not unlike one often voiced in judicial proceedings where the legal standing of psychological research is called into question. Legal cases are decided on an individual basis and so, even when the weight of evidence clearly supports the relevant social science generalization, the courts still require "proof" that it applies in the case being adjudicated. When judges ask psychologists to link the general principle to the specific case, it is difficult, if not impossible for them to do so with certainty. But that is what the law requires. Psychologists can provide relevant case knowledge and guidance, but the information they present is rarely, if ever, decisive in judicial decision-making.

Similarly, I know enough about psychology to be wary of psychological generalizations and the statistical methods used to analyze “supporting” data. You can never be entirely confident about the applicability of evidence derived from this approach. I have come to believe that psychology will always have to be content with this sort of limitation. Laws based on group means hold for some people, some of the time, but one never can be sure on any given occasion if they apply to a particular individual in the situation at hand.