Lies, damned lies, and BoingBoing; or why 42.03% is a dangerous number

A widely-read and widely-quoted post on BoingBoing said:

“Note 1: normal lifetime incidence in U.S. is about 42% (of developing any cancer). The increase in risk, i.e. 1 in 30 for 3,000 mSv (300 rem), changes the 42% to 42.03% chance of getting cancer in the exposed individual’s lifetime.”

1 in 30 = 3.3%, not 0.03%. Saying 42.03% understates the increased risk by two orders of magnitude. But BoingBoing trumpets the author’s credentials, highlights the sound bite which falsely trivializes the cancer increase, and ignores the numerous comments pointing out the error.

If you want to reassure me, you’re not going to do it by lying about the math.

Here’s another way of looking at it. Suppose you’re the Japanese government, trying to decide whether to expend the resources to evacuate 300,000 people from a hot zone where they’d receive a 3000 mSv cumulative dose over the next year. It might be nice to know whether the consequence of inaction is 10,000 additional people getting cancer or 90 additional people getting cancer. Math matters.