Harvard Public Health Review
Fall 2004




Assessing Risk

Smart health and safety choices are guided by quantitative research

Antibiotic resistance. Air pollution. Sexually transmitted disease. Infectious agents that endanger the food supply. These are but a few examples of threats to public health with which society must grapple using limited funds, labor, and expertise--and where decisions must be made despite incomplete data and uncertainty about the consequences. Helping government, industry, and consumers make such choices is the mission of the Harvard Center for Risk Analysis (HCRA), where faculty members and researchers use quantitative methods to analyze public health issues ranging from AIDS to mercury emissions to Mad Cow disease.

"Ideally we'd like to have all the information we need before acting," notes James Hammitt, HCRA's director and professor of economics and decision sciences in the Department of Health Policy and Management. "But that's not practical. Every decision--even the decision to do nothing until more research results come in--has consequences," he adds. "Often we have to choose before we have all the answers. We'd like to do so wisely."

Decision science attempts systematically and quantitatively to evaluate each choice for addressing a public health problem--its benefits and costs; its possible consequences; and the degree of uncertainty surrounding each of these. "Decision science strives to provide a complete accounting of the important consequences of a decision. The goal is to offer policy makers more insight into which choices will do the most good for the greatest number," Hammitt says.


In a world of limited resources, society must understand the clinical and economic implications of medical technology. The goal of HCRA's Program on the Economic Evaluation of Medical Technology (PEEMT) is to promote informed decision making by policy makers, payers, and health care providers in the use of medical procedures, drug treatments, devices, and preventive measures.

According to PEEMT's founding director, Milton Weinstein, an early pioneer of the decision science field, one powerful tool for controlling skyrocketing medical costs is cost-effectiveness analysis (CEA). PEEMT faculty can use CEA to evaluate and compare prevention and treatment options--including, for example, screening methods for cervical cancer, which in the developing world is the leading cause of cancer deaths in women. Also within PEEMT, Associate Professor Karen Kuntz builds computer simulations of colorectal cancer and other complex diseases. By calibrating them with large databases of information about real patients, these models become tools useful for shaping sound policies in disease prevention and care.

HCRA's faculty employ another methodology, benefit-cost analysis, to assess the pros and cons of various courses of action. For example, Senior Researcher Joshua Cohen used this strategy to evaluate a proposed ban on the non-emergency use of cell phones while driving. The "benefit" of a ban, he reasoned, would be a reduction in the deaths, injuries, and property damage related to motor vehicle crashes involving drivers distracted while phoning. The "cost" of such a ban could be expressed in terms of the net value drivers place on the calls a ban would force them to give up. Cohen found that a ban's costs and benefits were roughly equal: about $43 billion. His analysis has been used by several state legislatures as they considered restricting drivers' cell phone use.

The "costs" of a particular course of action are not only financial. Often they include increased risks to the environment and health as well. In assessing these risks, HCRA faculty consider the fact that policies designed to contain one risk may create others. To illustrate this concept, known as "risk-risk tradeoffs," Hammitt points to the widespread use of diesel fuel in some European nations. By putting lower taxes on this fuel, which burns more efficiently than gasoline, governments can reduce the carbon dioxide emissions linked to climate change.

But while diesel fuel may be good for the environment, it poses risks to human health, Hammitt says. The state of California proposes to regulate diesel fuel on the grounds that components of diesel emissions cause cancer. Even more dangerous, Hammitt notes, are fine particles from the exhaust, which have been estimated to cause ten times more deaths from other diseases.

Hammitt notes that all risks have two components, both of which must be assessed: probability (likelihood) and magnitude (size). The probability of contracting a lethal disease might appear low, one in 1,000, for example. But what if as many as 20 million people could potentially be exposed? The potential magnitude of the impact--20,000 deaths--might be unacceptably high.

In assessing risks, says Hammitt, "The question is: In order to reduce a risk, how much do we have to give up? What price will we have to pay in terms of dollars, increases in other risks, or goods and services we care about?" The answer, he says, is society's judgment call-- a decision ideally exercised with as complete an understanding as possible of its potential benefits and harms.


HCRA's work itself entails risk--the risk of controversy attached to some of the health and environmental issues HCRA investigates. While its studies are objective and peer-reviewed, representatives of government, industry, and consumers argue for or against HCRA's findings depending on their values and agendas. "We've been accused of being in league with groups on opposite sides of the same issue," says George Gray, HCRA's executive director and leader of an investigation of the Mad Cow threat to the United States beef industry (click here to see article).

HCRA has also been criticized by some who think it inappropriate to value human health in dollar terms as a guide to public health policy. But as Hammitt sums up, "Decision analysis provides a neutral, comprehensive, analytic approach that, when carefully applied, can provide important insights into which choices will do us the most good. I don't know of a better alternative."

As the following stories illustrate, decision science has the potential to impact the health of millions.

Corralling Mad Cow
Amid controversy and media hype, HSPH's analysis of risk to the U.S.
suggests the disease's spread would be limited

Fishy Business
As mercury levels rise, what are the risks and benefits of eating fish?h benefits

What Price Health?
Cost-effectiveness analysis seeks to maximize health care dollars.

Keeping Risk in Perspective
Communication helps public separate real dangers, false alarms.

Karin Kiewra is Editor of the Harvard Public Health Review and Associate Director of Development Communications at the Harvard School of Public Health




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