Evolutionary Health
Co-Evolution of Disease & Living Conditions
Health Effects
What is Risk?
Environmental Risk
Risk Assessment
Risk Abatement
Risk Perception
Risk Management
Uncertainty & Other Features of Risk Assessment
Precautionary Principle
Appendix 1: Contaminants
Appendix 2: Environmnet & Reproductive Health
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Uncertainty and Other Features of Risk Assessment


Every step of Figure 4 is fraught with uncertainties in the data. Thus while risk assessment is, in principle, an analytical way to get an idea of he magnitude of the impact of a hazardous or risky activity, the actual execution is hard. Some of the uncertainties were pointed out in the groundwater example.

There is also the fact that different people or groups may have different susceptibilities. For example, children or the elderly may be particularly vulnerable to certain air pollutants because of their limied or diminished lung capacity. All these aspects need to be considered and described in a total risk assessment. Different people may also have different value systems.
Risk assessment comes under heavy criticism for many reasons. Evidence in many areas of the assessment is often weak, and must be extrapolated, deduced, or otherwise guessed, and numbers that are chosen to be plugged in vary widely from assessor to assessor. Sometimes that variability can be attributed to the assessors' motivation, levels of expertise in a given subject area, or past experiences.

In 1990, eleven European nations each assembled their most experienced risk assessment teams to conduct independent analyses of a small ammonia production plant. The motivation of this exercise was to determine how closely the outcomes of each team's risk assessment of this relatively simple industrial facility would resemble each other. These assessors had no financial interest in the outcome; they were only hired to do their best assessment of the risk in this situation. The results of this exercise were astounding. Without any intentional manipulation of the assumptions in the analysis, the assessments of the hazards by different teams varied by factors as great as 25,000!

W. Ruckelshaus, administrator of the U.S. EPA under Presidents Nixon and Reagan, once said, "We should remember that risk assessment data can be like the captured spy: If you torture it long enough, it will tell you anything you want to know." He made this statement with the intent of promoting the use of risk-benefit analysis within the EPA!

The scientific nature of the risk assessment paradigm leads to possible misperceptions: (1) the numerical nature of the exercise conveys an impression of certainty even when the probabilistic nature is known; (2) scientists are considered experts even when the science is uncertain. The system under which scientists operate is one in which certainty and definite proof of existence are the highest values. Thus if an agent is suspected but not proved to be harmful, the scientists’ training would have the scientists say there is no harm rather than that there is harm. This proves a problem when we consider, for example, that we would rather err on the side of caution when considering environmental risk. Such tensions often hold up decision making and give polluting industries the benefit of the doubt, and result in causing harm.

Some agencies including the European Environmental Agency, and to a smaller extent, the U.S. EPA, have begun to adopt a more “precautionary” or preventative approach to risk rather than risk management after definite proof of harm. Pollution prevention and green design are examples of this philosophy.




  ©Copyright 2003 Carnegie Mellon University
This material is based upon work supported by the National Science Foundation under Grant Number 9653194. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.