It's always a little irksome to see or hear 'X causes Y% of cancer' because, really, it is the kind of culturally partisan gibberish that has made it possible for disreputable genetics testing companies to make all kinds of ridiculous claims.
Yes, you are more likely to get lung cancer if you smoke than if you don't, but lots of people get lung cancer who do not smoke and were never asbestos workers.
Writing on Discover, science journalist Ed Yong makes sense of those population attributable fractions (PAFs) - like what percentage of cases of a disease would be avoided if a risk factor was avoided.
From answering enquiries and talking to people, I reckon that your average reader believes that we get these numbers because keen scientists examined lots of medical records, and did actual tallies. We used to get questions like “How do you know they didn’t get cancer because of something else?” and “What, did they actually count the people who got cancer because of [insert risk factor here]?”No, they didn’t. Those numbers are not counts.
Those 2 million cases don’t correspond to actual specific people. I can’t tell you their names.
Instead, PAFs are the results of statistical models that mash together a lot of data from previous studies, along with many assumptions.
Good stuff, and a terrific overview of what scare journalism numbers really mean.
What does it mean to say that something causes 16% of cancers? by Ed Yong, Discover
