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Chaos theory was originally a branch of mathematical physics developed in 1963 by Edward Lopez. It deals with events and processes that cannot be modeled or predicted using conventional mathematical laws and theorems, such as those of probability theory or biostatistics. Chaos theory is concerned with finding rational explanations for such phenomena as unexpected changes in weather. The theory assumes that small, localized perturbations in one part of a complex system can have widespread consequences throughout the system. The vivid example often used to describe this concept, known as the "butterfly effect," is that the beating of a butterfly's wings can lead to a hurricane if the tiny turbulence it causes happens to generate a critical combination of air pressure changes. The key word here is "if," and much of chaos theory is concerned with attempts to model circumstances based on this conditional conjunction. Unpredictable events in medicine, such as the course of certain cancers and the fluctuations in frequency of some diseases, may be attributable to chaos theory.

Toward the end of the twentieth century, humankind began to face a crisis that required comprehension of chaos theory. A complex set of natural and human-induced changes in global ecosystems—global climate change, stratospheric ozone attenuation, species extinctions and reduced biodiversity, social and demographic turbulence, economic globalization, technological revolutions in communications, violent regional conflicts, and political instability—began to have far-reaching implications. These factors all interact in complex ways that impact on human health and well-being and could cause dramatic changes in the prevailing patterns of health and disease. Public health policies and long-range plans require certain assumptions about the likelihood that events will occur in accordance with known trends about which data and information exist. Such plans tend to be based on extrapolations of trends, such as population numbers and age distributions, and the impact of specific diseases are projected.

Scenarios in long-rang health planning need to take chaos theory into account if they are to cover all possible contingencies. For example, in long-range health plans for the application of technology to the diagnosis and treatment of cancers or coronary heart disease, one or more scenarios must take into account the possibility of innovative technical breakthroughs. This approach to long-range health plans has benefited from lessons learned by the oil and petrochemical industries in the 1970s, when only one major oil company was prepared for a sudden reduction in the available crude oil supply. This company's plans had included supply change as one possible scenario. In the health sector, long-range plans are flawed if they do not allow for chaotic events.

JOHN M. LAST

(SEE ALSO: Catastrophe Theory; Planning for Public Health)