Steve Kass

Year after year, thousands of Americans are devastated to discover that their community has been stricken by a disease cluster. Some rare and frightening disease of unknown cause has visited their community like a plague. Residents are afflicted at rates many times the national average.

Despite years of study, billions of dollars, massive lawsuits and at least two Hollywood movies, little progress has been made towards understanding, let alone preventing, disease clusters.

The general public continues to suspect and blame environmental causes, especially chemicals with names that are hard to pronounce. The real reason for most disease clusters is likely something else.

Math.

Yes, math. Look at this map.

This map shows the 2009 rate of aleatorum gravis, an emerging and debilitating disease that currently affects only one American in 5,000. In some communities, however, the disease is rampant. Counties with rates more than five times the national average are shaded in red, and those with more than twice the national rate are shown in the darkest shade of green. [Click on the image or here for the full U.S. map.]

Nebraska.

Clusters of a. gravis are concentrated in the nation’s heartland, especially Nebraska and neighboring states. Why? If you wanted, you could look for and find potential causes alarmingly close to each cluster. A gas pipeline, a chicken farm, a power plant, a landfill. Or you could have a lawyer look for you.

Look as hard as you want, but the fact is that the cause of these disease clusters is mathematics. There is no such thing as a. gravis. The map shows the result of randomly giving each U.S. resident the disease with a 1-in-5,000 chance. (Mathematica notebook and links to population and geographic data files available on request.)

Math, indomitable math, caused these clusters.

Randomness.

Cases of non-communicable disease come in clusters just by chance. So do bags of M&Ms that have more blues than average, but it’s hard to drum up fear about them. Randomness and uniformity are not the same thing.

By chance alone, some counties will end up with higher rates of any randomly-occurring disease than other counties. The Central Limit Theorem proves it. Which counties is anyone’s guess, but because of the Law of Large Numbers (not subject to repeal), small counties are more likely than large ones to end up with unusually high (or low) rates. Sanity check: When was the last time you read about a disease cluster the size of a large city, as opposed to a census tract, county, or neighborhood?

Science.

Do some diseases have non-random environmental causes? Sure. Cholera, to give a famous example. That’s why local and national governmental agencies like the CDC and the National Cancer Institute take reports of disease clusters seriously. But the good scientists there also understand the math, and I trust their advice about public health policy more than what I hear on the local newscast, on Oprah, or from yet another celebrity non-scientist.

Reminder: John Snow was a scientist. (He also drew a map to make his point, which was a darn good idea.)

By the way, you don’t even have to be in a red county to jump on the bandwagon of fear and woo. You can still decide your neighborhood is a disease cluster (when it’s not), get everyone riled up, and make a scary video. Or you can write for a shameful woo-purveying media giant. For free. Specifically, the one behind the recent stench of pseudoscience in the air about disease clusters, and who’s getting no link from here. If the miasma theory of disease were true, scientists would be dropping like flies from what they read.

Pseudoscience and pandering to unjustified fear waste society’s resources and sidetrack scientists from research that might make the world a better and less scary place.