Academic journal article Law and Contemporary Problems

How Much Evidence Is Enough? Conventions of Causal Inference

Academic journal article Law and Contemporary Problems

How Much Evidence Is Enough? Conventions of Causal Inference

Article excerpt

I

INTRODUCTION

One of the most important issues for science in the courtroom is the determination of causality. Like science in the courtroom, science in the regulatory arena can also bring a clash of cultures, misunderstanding, and controversy--especially when decisions must be made with some urgency with interested parties watching closely. In this article I will discuss some conventions in the conduct of science and in the ways that scientific information is communicated to nonscientists that can make it difficult for judges, lawyers, regulators, and politicians to do their jobs making decisions about complex environmental and health issues.

Of particular concern are the methods and conventions of causal inference as they are applied to controversies over whether chemicals and technologies are harming human health and the environment. There are far too many examples of environmental hazards that were permitted to be produced long after the evidence for harm was substantial. (1) Political and economic forces are partly to blame for many of these cases, but scientific methods--particularly methods of causal inference--could be improved to make it easier for society to assess when evidence of a hazard is sufficient to take action. This article briefly describes some of the different conventions of causal inference in different scientific fields. As opposed to that in "pure" sciences, causal inference in environmental health sciences must necessarily include consideration of the social responsibility to act in the face of uncertainty, which has implications for the scientific process. A key component of environmental health sciences, distinct from many other science disciplines, is the management and communication of uncertainty. This article presents some examples of how this might improve the contributions of science to environmental health problems.

II

SETTING THE CONTEXT--WHAT'S SPECIAL ABOUT ENVIRONMENTAL HEALTH SCIENCE?

Most of the important environmental health crises share a fundamental characteristic: they appear to arise from disruptions of natural systems or cycles, whose behaviors are only partially understood. (2) Global warming, endocrine disruption, ecologic and health risks from genetically modified organisms, environmental breast-cancer risks--these are all hazards about which a great deal of uncertainty remains. Martin Krayer von Krauss, a scholar of policy applications of science, characterizes the problems this way:

   There is not one problem, but a tangled web of related
   problems[:] ... The dynamics of the systems studied are not
   necessarily regular, but are characterized by synergistic [or]
   antagonistic relationships [or both], indirect relationships, long
   delay periods between cause and effect, [and] thresholds, or
   non-linear behaviours[.] The issue lies across or at the
   intersection of many disciplines[.] ... [I]t has economic,
   environmental, socio-cultural, and political dimensions.... (3)

Because the human body, an ecosystem, a human society, or an economy are all complex dynamic systems, their behaviors are subject to fundamental uncertainties that will not be reduced no matter how long they are studied. This characteristic of complex systems sets them apart from many of the problems that western science has so successfully conquered. This inherent complexity is one defining feature of the terrain in which the environmental health sciences operate.

A second defining feature is the urgency to act to prevent harm; the environmental health sciences look more like medicine in this regard than, say, astronomy or geology. Public-health scientists often do not have the luxury of waiting for further study to tie up the loose ends before the need to act. In other words, science conducted to inform policy on disease prevention and environmental protection is different from that of most conventional science in fundamental ways: facts are uncertain, social values are in dispute, the stakes are high, and decisions are urgent. …

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