Today's post, Useless Medical Disclaimers was originally published on March 19, 2007. A summary (taken from the LW wiki):

Medical disclaimers without probabilities are hard to use, and if probabilities aren't there because some people can't handle having there, maybe we ought to tax those people.

(alternate summary:)

Eliezer complains about a disclaimer he had to sign before getting toe surgery because it didn't give numerical probabilities for the possible negative outcomes it described. He guesses this is because of people afflicted with "innumeracy" who would over-interpret small numbers. He proposes a tax wherein folks are asked if they are innumerate and asked to pay in proportion to their innumeracy. This tax is revealed in the comments to be a state-sponsored lottery.

Discuss the post here (rather than in the comments to the original post).

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A possible compromise solution to the problem of scaring people with probabilities would be to use precisely defined words instead, so

  • "definite possibility" = 0.1 <= P < 0.01
  • "small possibility" = 0.01 <= P < 0.001
  • "tiny possibility" = 0.001 <= P < 0.0001
  • etc.

Then the disclaimer could say: "There is a small possibility of infection(*)", and the details could be in a footnote.

Patient information leaflets in the UK contain precisely this information on side-effects (which order of magnitude the frequency of the side-effect is). Giving the actual numbers, rather than an ambiguous wording, for surgery would be useful if there's sufficient data.

If I recall correctly, the IPCC used a similar system for climatology predictions. It worked well there, too.

[Edit: To be precise: by writing the conclusions of their report using specified English-language terminology to express degrees of certainty, they were able to write a rhetorically-compelling account that incorporated quantitative probability data. The quality of these data is irrelevant to the example.]

Why not just use the footnote? Just say:

There is a possibility of dying from a meteor*.

*1 in 700,000

If you have to read the footnote to tell what "small" means anyway, why bother writing it?

I like this idea, but the phrase "definite possibility" sounds a bit odd, it's almost an oxymoron. How about "significant possibility" instead?

Or "distinct possibility".

That works even better, I think.

The problem can't just be that people won't realize how small it is if they give you the number, because they don't use numbers when they're warning about drunk driving etc. I feel like I'm the only one who'd like data in the form of "Every time you drive drunk, your expected lifespan is decreased by X per mile, the expected lifespans of each other person in the car with you is decreased by Y per mile, and the total of the bystanders' expected lifespans are decreased by Z per mile", possibly also giving probabilities for if you get drunk and you might drive, if you get drunk and you walk, if you're in an urban, suburban, or rural area, etc.

I have heard rumors to the effect of "your expected lifespan decreases by X minutes for each cigarette you smoke", though I've never been told that by a reliable source.