The World Health Organization appears to exist primarily to give newspaper editors the excuse to run senational headlines about the risk of cancer. This is not a repeat story from earlier years. Oh, wait. Yes it is. Here’s The Atlantic‘s Ed Yong to de-sensationalize the recent scary headlines:
The International Agency of Research into Cancer (IARC), an arm of the World Health Organization, is notable for two things. First, they’re meant to carefully assess whether things cause cancer, from pesticides to sunlight, and to provide the definitive word on those possible risks.
Second, they are terrible at communicating their findings.
Group 1 is billed as “carcinogenic to humans,” which means that we can be fairly sure that the things here have the potential to cause cancer. But the stark language, with no mention of risks or odds or any remotely conditional, invites people to assume that if they specifically partake of, say, smoking or processed meat, they will definitely get cancer.
Similarly, when Group 2A is described as “probably carcinogenic to humans,” it roughly translates to “there’s some evidence that these things could cause cancer, but we can’t be sure.” Again, the word “probably” conjures up the specter of individual risk, but the classification isn’t about individuals at all.
Group 2B, “possibly carcinogenic to humans,” may be the most confusing one of all. What does “possibly” even mean? Proving a negative is incredibly difficult, which is why Group 4 — “probably not carcinogenic to humans” — contains just one substance of the hundreds that IARC has assessed.
So, in practice, 2B becomes a giant dumping ground for all the risk factors that IARC has considered, and could neither confirm nor fully discount as carcinogens. Which is to say: most things. It’s a bloated category, essentially one big epidemiological shruggie. But try telling someone unfamiliar with this that, say, power lines are “possibly carcinogenic” and see what they take away from that.
Worse still, the practice of lumping risk factors into categories without accompanying description — or, preferably, visualization — of their respective risks practically invites people to view them as like-for-like. And that inevitably led to misleading headlines like this one in the Guardian: “Processed meats rank alongside smoking as cancer causes – WHO.”