Understanding Health Risk Calculations

Understanding Health Risk Calculations

Health risks are all around us. They are present all the time, even when we sleep. Understanding our chances of being affected by one risk or another is a little like understanding our chances of winning the lottery. Numbers are often used to describe both our health risks and our chances or probability of winning the lottery, but this is where the similarity ends.

When you buy a lottery ticket, your chances of winning depend on the number of possible combinations of numbers, not on whether you pick your favorite lucky numbers. Every time you buy a ticket, day after day, you have the same chance of winning, so your chance may always be, for example, one in a million. Nothing you or anyone else can do, short of cheating, can change that chance.

Your chance of getting cancer from exposure to a chemical, however, like your chance of being killed in a vehicle accident, is not as easy to understand. This is because conditions that affect your chance are always changing. In the case of a vehicle accident, the road may be slippery, you or another driver may be drunk, your car or another vehicle may get a blow out at high speed, someone may fall asleep at the wheel, someone may throw a rock from an overpass, or an airplane may fall from the sky. All of these conditions and many more affect the chance of being involved in an accident. Sometimes you can control the conditions effectively, but most of the time you can't.

Your chances of getting cancer from exposure to a certain chemical also depends on different circumstances or conditions. How long and the frequency at which you are exposed to a chemical, the amount or concentration, your own personal "make up" or susceptibility, and age are only a few of the variables to be considered when calculating your risk. Some of these conditions you can control, some you cannot.

When a scientist calculates risks, she or he uses different types of numbers to represent different types of risks. For the risk of someone getting cancer from exposure to a certain chemical at a certain level over the course of a lifetime, there is no way to calculate an individual's exact chance. The best that a scientist can do is to calculate the chance of cancer occurring among, say, one million people.