Eugine_Nier comments on Hearsay, Double Hearsay, and Bayesian Updates - Less Wrong

47 Post author: Mass_Driver 16 February 2012 10:31PM

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Comment author: [deleted] 19 February 2012 04:28:15PM *  0 points [-]

The original question was:

Is there any evidence than American or any other legal system is significantly better than chance at what it does?

which I would interpret as ‘Is P(Conviction|Guilt) substantially larger than P(Conviction|Innocence)?’ Now, for some crimes such as copyright infringement, P(G) is very close to 1, so P(C|G) cannot be close to 1 simply because then there wouldn't be enough room in prisons to hold NP(C|G)P(G) people (N being the population -- times the mean sentence length, over the mean lifespan, and possibly some other factor of order unity I'm forgetting of), and since P(I) is small, in order for P(C|I) to be much less than P(C|G), P(C and I) = P(C|I)P(I) must be very small.

(Also, we want the system to be unbiased, i.e. P(C|G, brown skin) to be close to P(C|G, pink skin), P(C|G, penis) to be close to P(C|G, vagina), and so on, and so forth. The best way of achieving this would IMO be for all of these numbers to be close to 1, but that's impossible with the current definition of G and finite capacity of prisons.)

Comment author: Eugine_Nier 19 February 2012 09:52:43PM 2 points [-]

‘Is P(Conviction|Guilt) substantially larger than P(Conviction|Innocence)?’

Are we restricting to cases that are prosecuted or doing this over all people?

Comment author: [deleted] 19 February 2012 10:23:35PM 0 points [-]

The immediately obvious answer would be “over the prosecuted if you're only ‘testing’ the courtroom itself, over all the people if you're ‘testing’ the whole system”, but I'm not sure what the ‘ideal’ thing for a courtroom to do in terms of P(C|Prosecution, G) and P(C|P,I) if the police is ‘non-ideal’ so that P(P|G) is not close to or greater than P(P|I) to start with. Or even whether this question makes sense... I'll have to think more clearly about this when I'm not this tired.