The Arithmetic of Human Behavior

The human world is different from other natural phenomena after all, although the difference is not in any way beyond the reach of rationality. Human behaviors are responses to information, and unlike physical forces, information does not force things. Input-output connections, made in the mind, are as diverse and changeable as the minds that contain them. On one hand this produces uncertainty—with one input leading to many outputs. But on the other hand this allows us to efficiently utilize disjunctive mechanisms—with many inputs leading to one output—and produce reliable outcomes in spite of uncertainty.

There is, however, a mismatch between the logic of these disjunctive mechanisms (A or B or C…leads to D), and the conjunctive logic (A and B and C…leads to D) of the reasoning we generally rely on. And there is an allied mismatch between ideals, traditions, and methods that have thrived using conjunctive reasoning and that prize explaining the most with the least, and what understanding human behavior requires. We strive to explain mechanisms that are by nature prolific and diverse in the most parsimonious and unified terms. This blinds us to much of how the human world works and leads us to accept overly abstract and unrealistic understandings—from stereotypes to sophisticated social science theories and models.

This book explores misunderstandings arising from these mismatches and what can be done to correct them: in general understandings, decision making and planning, research methods, and quantitative analysis. A practical problem is that we cannot readily replace conjunctive understandings with disjunctive ones. Our minds are not built to handle the myriad possibilities, probability estimates, calculations, and data handling required by disjunctive explanations. In the section on qualitative solutions the book discusses strategies that work within our limitations.

When the data collection and computational resources are available disjunctive systems can be tackled head-on. The section on quantitative solutions present a statistical approach, called Disjunctive Mapping, whose analyses are based on computing the sums of the probabilities of the various ways outcomes occur, and measuring the influence of individual factors in the contexts of each of those ways.