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Lumifer comments on Open thread, 25-31 August 2014 - Less Wrong Discussion

4 Post author: jaime2000 25 August 2014 11:14AM

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Comment author: Lumifer 28 August 2014 06:20:33PM -1 points [-]

but there's a 50% chance the test detects the difference and a 50% chance it doesn't

Rationality is not a binary variable, but continuous. It is NOT the case that the test has a chance of detecting something or nothing: the test will output a value on some scale. If the test is not powerful enough to detect the difference, it will show up as the difference being not statistically significant -- the difference will be swamped by noise, but not just fully appear or fully disappear in any given instance.

You'll either get a lot of results that average 20% less or a lot of results that aren't less at all

Nope -- that would only be true if rationality were a boolean variable. It is not.

Comment author: Jiro 28 August 2014 06:26:59PM 1 point [-]

That doesn't follow. For instance, imagine that one group is irrational because their brains freeze up at any problem that contains the number 8, and some tests contain the number 8 and some don't. They'll fail the former tests, but be indistinguishable from the first group on the latter tests.

Comment author: Lumifer 28 August 2014 06:33:11PM 2 points [-]

I can imagine a lot of things that have no relationship to reality.

In any case, you were talking about a test that has a 50% chance of detecting the difference, presumably returning either 0% or 20% but never 10%. Your example does not address this case -- it's about different tests producing different results.

Comment author: Jiro 28 August 2014 08:11:54PM 0 points [-]

You were responding to Stefan. As such, it doesn't matter whether you can imagine a test that works that way; it matters whether his uncertainty over whether the test works includes the possibility of it working that way.

Your example does not address this case -- it's about different tests producing different results.

If you don't actually know that they freeze up at the sight of the number 8, and you are 50% likely to produce a test that contains the number 8, then the test has a 50% chance of working, by your own reasoning--actually, it has a 0% or 100% chance of working, but since you are uncertain about whether it works, you can fold the uncertainty into your estimate of how good the test is and claim 50%.