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JoshuaFox comments on Open thread, May 17-31 2013 - Less Wrong Discussion

2 [deleted] 17 May 2013 01:47PM

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Comment author: JoshuaFox 19 May 2013 07:58:08AM *  3 points [-]

What do people mean by this sort of probability estimate, this one from Angelina Jolie's NYTimes article? "My doctors estimated that I had an 87 percent risk of breast cancer and a 50 percent risk of ovarian cancer, although the risk is different in the case of each woman" (Italics added.)

Do they mean:

  • "Don't mistake a high probability for certainty. In particular, don't accuse me of misleading you if I state a high probability and the outcome does not occur."
  • "Don't think that because the probability of a bad outcome is less than 100%, you can do some wishful thinking and ignore the risk."
  • "With a little effort, we could acquire more evidence allowing us to refine the probabilities for your case."
  • Or something else?

Often, if you ask someone for the probability (or frequency) of some outcome based on their experience with a given reference class, they refuse to give a number, likewise saying that "each case is different." In these cases, a fourth reason is possible, namely that they are too lazy to do the estimation.

I understand that not everyone is a Bayesian black-belt, but I am trying to figure out what implicity assumption motivates people to talk this way.

Comment author: satt 19 May 2013 04:45:03PM 6 points [-]

I assumed it was just a way of saying different women fall into different reference classes for the purposes of estimating breast cancer risk (e.g. an alcoholic woman with a positive BRCA1 test result and a vitamin D deficiency vs. a teetotaller with no harmful BRCA mutations and no vitamin deficiencies).

Comment author: JoshuaFox 20 May 2013 07:33:12AM 4 points [-]

Thanks, I think that's it. She means "medical science has given us more detailed results than just a blanket probability across all female humans. Using various sorts of information, doctors can give each woman a more refined probability estimate."

Comment author: Zaine 19 May 2013 12:23:43PM 3 points [-]

There is no implicit assumption. She was apparently tested for BRCA1 based on family history, and was found positive. The correlation between BRCA1 and those cancers yields a certain percentage of risk, a calculation into which family history might also account. She links to here: http://cancer.stanford.edu/information/geneticsAndCancer/types/herbocs.html

Your third option is correct - although both effort, will and resources to acquire genetic testing are required.

Comment author: JoshuaFox 20 May 2013 07:33:55AM 2 points [-]

Yes, you got it. She's saying "If you go to your doctor and do some tests, you can get an estimate targeted at you."

Comment author: ChristianKl 23 May 2013 12:38:26PM 2 points [-]

Do they mean:

Who's they? You are reading a text written by Angelina Jolie for a general audience. She has to make certain that no woman reader who reads the story comes away with thinking that she also has a 87 percent risk.

I understand that not everyone is a Bayesian black-belt, but I am trying to figure out what implicity assumption motivates people to talk this way.

What does a Bayesian black-belt do, when the only numbers he has are come frequentist statistics that someone else did?

Comment author: JoshuaFox 20 May 2013 07:38:54AM *  1 point [-]

Thanks, satt and zaine answered it.

Introspecting a bit, I realize that my question was motivated not sy Angelina so much as by various refusals I have encountered to give a probability/frequency estimate, even when people are well-positioned to give one.

I think it is often motivated by a tendency to withhold information in order to maintain power in human interaction; but in many cases its the first and second options above.