Lumifer comments on What Bayesianism taught me - Less Wrong

62 Post author: Tyrrell_McAllister 12 August 2013 06:59AM

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Comment author: Lumifer 12 August 2013 05:30:26PM 0 points [-]

Most of the creatures in that class have, in fact, not been mentioned by you or anyone else.

True. But then I can write a one-line Perl script which will bring into being evidence for a LOT of monsters.

Which itself brings into being the question of what kind of evidence the output of a RNG is. Or, perhaps, what kind of evidence does software produce.

Comment author: Jiro 12 August 2013 06:06:51PM 4 points [-]

I'd think that how much mentioning a monster updates the probability that it exists depends on the context of mentioning the monster. Furthermore, mentioning it in the context of examples of probability should score particularly low in this regard.

Comment author: Lumifer comment score below threshold [+] (6 children)

Comment author: Jiro 12 August 2013 08:46:38PM * 4 points [-]

If you wrote a short story about a monster, there's some chance that the monster exists, there are legends about it, one of those legends made its way to you, and you then chose to use it in your story. Thus, if I never heard of the monster, then you wrote such a story and I had no further information about your story-writing process, that would indeed increase my estimate that the monster exists by a miniscule amount.

If you wrote the story specifically to prove a point in a lesswrong discussion about monster names that are pulled out of thin air, that would be further information, so my estimate wouldn't increase in the same way.

Moreover, it's not twice the evidence anyway, since the story and the lesswrong post aren't independent.

Comment author: Viliam_Bur 18 August 2013 02:48:21PM 3 points [-]

Oh, an now we have TWICE the amount of evidence for Ygafalkufeoinencfhncfc compared to what we had a few minutes ago. Can we extrapolate the trend?

Note: It's not a linear trend. If you mention the name one million times, it does not make it one million times as likely. Also, being mentioned one million times by the same person is not the same evidence as being mentioned by one million people, once by each. And even that is not a linear trend.

Comment author: Lumifer 19 August 2013 06:07:28PM -2 points [-]

It's not a linear trend.

Nobody said it was. In any case, I was talking about the amount of evidence, not about what does that imply in terms of belief probabilities.

A "linear trend" in probabilities would have big issues, of course, because there are hard caps at zero and one.

Comment author: Viliam_Bur 24 August 2013 01:31:51PM 2 points [-]

We have some misunderstanding here. My best guess is that you think evidence makes something likely, while the typical usage here is that evidence makes things more likely. An example: Imagine that according to your best knowledge, some thing X has a probability 0.000001. Now you get some new information E, and based on all the knowledge you have now, the probability of X is 0.000001001.

On one hand, the information E increased the probability of X from 0.000001to 0.000001001. This is what we mean by saying that E is an evidence for X. It made it more likely.

On the other hand, even the increased probability is pretty close to zero. Therefore, more likely does not imply likely or even worth considering seriously (you can imagine even more zeroes before the first nonzero digit).

Similarly, probability of Ygafalkufeoinencfhncfc is pretty close to zero, but not exactly zero. Mentioning it on a discussion forum (choosing this specific topic instead of other millions of topic that could have been chosen) slightly increases the probability (at the cost of those other topics that were not chosen to be mentioned). The change is very small, but technically it is an increase. That's why we call it evidence for Ygafalkufeoinencfhncfc.

Comment author: Lumifer 27 August 2013 04:57:53PM -1 points [-]

I understand the argument. I don't accept it.

Comment author: Mycroft65536 13 August 2013 04:58:14PM 2 points [-]

No. We can't extrapolate a trend. That's what"You cannot expect that future evidence will sway you in a particular direction" means.

Lumifer comments on What Bayesianism taught me - Less Wrong

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