Here is a recent story from the NY Times about the dangers of processed meat. (Thanks to Michael O’Hare for pointing this out)
We see a 4 percent increase in the risk of cancer even at 15 grams a day, which is a single slice of ham on a sandwich,” said Dr. Nigel Brockton, director of research for the American Institute for Cancer Research.
Eating a more typical serving of 50 grams of processed meat a day would increase the risk of colorectal cancer by 18 percent, a 2011 review of studies found.
From what I understand, the background rate of colorectal cancer is roughly 4%. So one natural way of reading this passage is that if you eat one slice of ham per day your risk increases to 8%. And if you eat 3-4 slices per day, a more typical serving for ham lovers, your risk would increase 18% which, when added to the 4% background rate, brings your risk to 22%. In other words, according to this literal reading, over 20% of people who eat ham, bacon, pastrami, sausage, etc. every day get colorectal cancer.
This of course is nonsense. The incidence of colorectal cancer is no where near that high. The passage is systematically misleading.
What’s going on here is that the good doctor and the reporter for the Times are failing to describe how we should understand this data. It’s about relative risk not absolute risk, as the underlying research report makes very clear.
Let me explain:
If the background rate of colorectal cancer is 4%, an increase of 4% from one slice of processed meat per day is an increase of 4% relative to the background rate. 1.04 X 4=4.16. Your risk increases by less than a quarter of a percent. If you’re in that group that has a bologna sandwich packed with 4 slices everyday, your risk increases to 18% over the background rate. 1.18 x 4=4.72. Round it up to 5%. A really nasty habit of eating 50 grams, almost 3/4 lb. of deli meat per day, increases your risk of getting colorectal cancer about 1% over the background rate of 4%.
If you really love deli meats, isn’t that worth the risk?
I’m not suggesting that people eat as much processed meat as they want or that we should ignore health warnings. The cumulative effect of too many indulgences would indeed add up to an unhealthy diet. But if processed meat is one of your few guilty pleasures, surely a 1% increase in risk is not worth worrying about.
Yet, the headline says:
Is Eating Deli Meats Really That Bad for You?
Even small amounts of processed meat increase the risk of colorectal cancer.
The story goes on to point out all the chemicals that go into processed meats and the health warnings associated with them. Nowhere in the article is the small risk effect mentioned.
One would expect that reporters and editors who work for the NY Times would be aware of the difference between relative and absolute risk. Surely doctors and researchers know the difference. They also are quite aware that most readers are not sophisticated when it comes to statistics. Yet they make no attempt to correct the potential misreading.
Rather than worrying about eating that piece of salami that is beckoning, perhaps we should worry about why the NY Times is unnecessarily scaring people. Could it be because it’s click bait and sells advertising? They wouldn’t do that would they?