APMason comments on Open thread, October 2011 - Less Wrong

5 Post author: MarkusRamikin 02 October 2011 09:05AM

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Comment author: selylindi 14 October 2011 05:05:35AM 8 points [-]

On the Freakonomics blog, Steven Pinker had this to say:

There are many statistical predictors of violence that we choose not to use in our decision-making for moral and political reasons, because the ideal of fairness trumps the ideal of cost-effectiveness. A rational decision-maker using Bayes’ theorem would say, for example, that one should convict a black defendant with less evidence than one needs with a white defendant, because these days the base rates for violence among blacks is higher. Thankfully, this rational policy would be seen as a moral abomination.

I've seen a common theme on LW that is more or less "if the consequences are awful, the reasoning probably wasn't rational". Where do you think Pinker's analysis went wrong, if it did go wrong?

One possibility is that the utility function to be optimized in Pinker's example amounts to "convict the guilty and acquit the innocent", whereas we probably want to give weight to another consideration as well, such as "promote the kind of society I'd wish to live in".

Comment author: lessdazed 16 October 2011 07:26:03AM *  8 points [-]

A rational decision-maker using Bayes’ theorem would say, for example, that one should convict a black defendant with less evidence than one needs with a white defendant, because these days the base rates for violence among blacks is higher.

One would compare black defendants with guilty black defendants and white defendants with guilty white defendants. It's far from obvious that (guilty black defendants/black defendants) > (guilty white defendants/white defendants). Differing arrest rates, plea bargaining etc. would be factors.

Where do you think Pinker's analysis went wrong, if it did go wrong?

He began a sentence by characterizing what a member of a group "would say".

Comment author: APMason 16 October 2011 11:44:45PM 4 points [-]

Yes. It's important to remember that guilty defendants aren't the same thing as convicted defendants. A rational decision-maker using Bayes' theorem wouldn't necessarily put all that much weight on the decisions of past juries, knowing as we do that they're not using Bayes' theorem at all. And, of course, a Bayesian would need exactly the same amount of evidence to convict a black defendant as they did a white defendant. That question is whether skin colour counts as evidence.

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