Cyan comments on Bead Jar Guesses - Less Wrong

17 Post author: Alicorn 04 May 2009 06:59PM

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Comment author: Vladimir_Nesov 04 May 2009 08:26:45PM *  1 point [-]

Alicorn, I think it'd be appropriate to add the following link at the beginning of the article:

Related to: Priors as Mathematical Objects.

It also kinda answers your questions.

Even if Omega had asked about the bead being lilac, and you'd dutifully given a tiny probability, it would not have surprised you to see a lilac bead emerge from the jar.

I see this conclusion as a mistake: being surprised is a way of translating between intuition and explicit probability estimates. If you are not surprised, you should assign high enough probability, and otherwise if you assign tiny probability, you should be surprised (modulo known mistakes in either representation).

Predicting the second bead given the color of the first one can also be expressed as probability estimates for joint observations, made before you observe the color of the first bead. What is the probability that you'll see two reds? That you'll see a red followed by a non-red? Non-red following by a red? Two non-reds? Then crunch the numbers through the definition of conditional probability/Bayes' theorem.

Comment author: Cyan 04 May 2009 08:43:30PM *  0 points [-]

I see this conclusion as a mistake...

... but it isn't, because the degree of surprise doesn't just depend on the raw probability, but also only the number of other possible outcomes under consideration. That Omega uses the term "lilac" may reasonably be taken as evidence that the space of color outcomes should be treated as finely divided.

ETA: I guess the mistake is in comparing feelings of surprise across outcomes with the same probability embedded in event spaces with different cardinalities.

Comment author: JGWeissman 04 May 2009 09:09:05PM 1 point [-]

If Omega asked me the probability of the next bead being lilac, I would be surprised to if the next bead actually was lilac, in a way I would not be surprised to find the bead is turquoise, an event to which I assign equal probability, but was not specifically considering prior to the draw, as any higher probability set of events which excludes drawing a turquoise bead would seem artificial. If the first two beads are the colors Omega asks me about, my leading theory would be that Omega will draw out a bead of which ever color he just brought up. (The first draw would cause me to consider this with roughly equal probability as maximum entropy.)

Comment author: Vladimir_Nesov 04 May 2009 09:32:00PM 0 points [-]

the degree of surprise doesn't just depend on the raw probability, but also only the number of other possible outcomes under consideration.

Well, maybe it isn't, but it should.

Comment author: billswift 04 May 2009 10:05:58PM 0 points [-]

"doesn't just depend on the raw probability" - Correct. It also depends strongly on how reliable you think your estimate of the probability is. That is, your confidence interval.