Re: How can I compare risks?

People say that I am at greater risk of being hit by a car than struck by lightening. Or that I am not likely to get anthrax. How do they know? How can I figure it out for myself?

The short answer is that no one knows exactly how likely it is that bad events will happen, but we can make good guesses based on data. For instance, if we count the number of people hit by cars and the number struck by lightning in a year, we can get a rough idea of the chance of being hit by a car or struck by lightning. By studying different types of misfortunes, scientists can get rough ideas of how likely different types of risks are, and then create plans to deal with accidents and illnesses. Most of what we know about these risks is good ways to avoid them, for example, wearing a seat belt in a car or a helmet on a bicycle makes the chance of injury much smaller.

Many different types of scientists study future risks. For instance, actuaries study the chances that bad events happen so that insurance companies (like those that sell life and health insurance) can accurately charge their customers. Doctors study how differenct medicines and behaviors (like smoking) affect the chances of contracting diseases like lung cancer. Finding out the risks associated with certain behaviors can help people to avoid those behaviors and lower their chances of becoming sick. In the United States, the Centers for Disease Control and Prevention (the CDC for short) is always gathering information about illness in the U.S. in order to better help people to stay healthy. They have everything from information on this year's flu season to how various groups are responding to the anthrax scare.

In order to assess the risk from things such as lightning, you have to keep track of how many lightning related injuries and deaths occur over a long period. This can be tough. Within NASA, the Global Hydrology and Climate Group has a set of people they call the "Lightning Team" who collect and try to analyze data from lightning strikes. Not everyone who is hit by lightning reports the fact, and there is no national center where such data is collected, but they do their best to get accurate data. The National Highway Traffic Safety Administration has the responsibility for collecting information about automobile accidents and injuries, and their data is far more accurate.

For things like anthrax it is very difficult to determine the exact risk, other than to say that it is very, very low. Less than 20 people in the U.S. have become infected with anthrax (and most of those people will recover with treatment), whereas hundreds of thousands of people are injured in automobile accidents each year. Reading news stories about anthrax can make the problem seem worse than it is. Pay careful attention to the numbers involved in these stories, and you will see that they are very small.

Mark Huber