what is “increased risk”?

We hear in the news all the time about activities or substances (usually desirable) that increase the risk of something else (usually undesirable).

What we rarely (never?) hear about is what that actually means.

Basically, unless we know the starting odds and what the increase (or decrease) is, “increased risk” does not give most people enough information to know if they want to act on it.

For example — and I’m making up a ridiculous example so no one accidentally thinks that these are real stats — let’s say that in the general population, there is a 1% chance that your left foot will turn blue, probably in late adolescence.  (See, I’ve already made it less concrete by including the “probably.”)  Now, as the general population, unless we’ve done some research, we don’t know the exact incidence of blue foot: we know it’s kind of rare but we know people who it happened to.

A study comes out in the news: eating chocolate-covered celery increases your risk of blue foot by 10%.  Wow!  10%!  But really, this just means that now you have a 1.1% chance of getting blue foot.  Is it worth giving up chocolate-covered celery for that tiny amount?

New headline: “Drinking green carbonated beverages doubles your chances of blue foot!”  Doubles! Which really means that now you have a 2% chance of getting blue foot, half of which is uncontrollable.

The reverse is also true: “Getting 15 hours of sleep per night reduces your risk of blue foot by 25%”  So now we’re down to a 0.75% chance in exchange for sleeping through most of your life.

Do you see what I’m saying?  Yes, it is nice to know what things are bad for you and which are good.  In reality, most of these triggers (positive or negative) act for or against more than one ailment and generally disintegrate or improve overall health anyway.  (BPA is linked to more than just breast cancer, and carrots have more benefits than beta carotene.)  But there is quite a bit of leeway in the stats to make them sound more urgent than they perhaps really are.  Without knowing more numbers (or in some cases, any numbers), it is difficult or impossible to make data-driven decisions.

Of course, if you want to avoid blue foot at all costs, then ditching both the chocolate-covered celery and green carbonated beverages would not be a bad plan.  As long as you understand that that still leaves you with the original 1% chance.

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