Suppose most economists believe that “Libertarian economists can’t do math,” and that, on average, they are correct. How does this…

You say “1. The fact that jurors are supposed to assume that the guy in the dock committed the crime with probability 1/N, when everyone knows that it is really much higher than that, restrains cops who might otherwise exploit their power to get someone convicted on little evidence other than the fact that they were arrested.”

It is because juries do not *convict* people based merely on the fact that they are in the dock that constraints the police, DA, etc. But this does not require them to assign probability 1/N, or in other words, to ‘ignore plain facts’, because a decision requires not just a probability distribution but also a loss function. To obtain the desired decision, the loss associated with convicting an innocent person must be greater than a threshold, the threshold being determined by the loss associated with freeing a guilty person and the probability of being guilty given only that you are in court.

illywacker;

I’d be astonished if, having learned that the guy he checked in was Atta, the CSA didn’t think he looked suspicious in retrospect.

Would it have been more socially destructive to have avoided 3000 deaths plus the Iraq war by using ethnic profiling?

For details, see:

http://isteve.blogspot.com/2006/09/political-correctness-saved-mohammed.html

What I’m driving at is that quite often, in the sort of intelligence/policing scenarios that this usually affects, it’s beneficial to set the barrier for action high – like turning down the sensitivity of a radar in order to get rid of clutter or using a band-pass filter to get rid of radio noise.

Well, to be accurate, jurors *do* act on that assumption. They’re instructed not to, which (we hope) reduces the tendency. Also, the knowledge of the general population that cops and DAs *don’t* show complete restraint (partly because of jurors’ imperfect impartiality) reduces the tendency a bit more. So there’s an equilibrium there, and a dynamic one, since jurors’ level of impartiality is determined by their perception of cops’ restraint, which has a substantial time lag from actual changing levels of police restraint. You might even expect there to be cycles around the equilibrium point.

There exists a rule that says: to get a conviction, the case must be proved in court beyond a shadow of a doubt. Because that rule exists, cops are reluctant to arrest and DAs unlikely to press charges unless the case can be proven on its own merits. Since cops and DAs act that way, it seems safe to assume most people who get arrested and accused of a crime are probably guilty.

But if jurors start acting on the assumption that people against whom charges have been brought must be guilty, they destroy the incentive for cops and DAs to show restraint. The more people make use of the “he’s probably guilty” rule of thumb in /current/ cases, the less valid it will be in /future/ cases.

So we have some knowledge about what is probably true given our current set of social institutions, but it’s not safe to act on that knowledge as a hard rule, because acting on it destroys the contingency that produced it.

#1 advances the policy of disgarding age or race descriminations in arrests, which is probably a good idea. People should be judged on what they are doing and where they are located at the scene of a crime, not external features like race.

Part of the problem is that race is the most readily distinguishable human characteristic aside from sex and general stage of life, so that it tends to be overweighted in many judgements, especially those of guilt. Us humans have a millenia-old history of xenophobic cultural tendencies, which can be tapped to turn anyone against anyone else if the situation calls for it, and causes major problems both a local and national leevel when allowed to flourish.

#2 is true, but also partially beside the point because there is always descrimination in employment, no matter what. So nothing can be changed.

#3 is the theory that racial profiling in the police force operates like a bigot magnet. I believe that the police force already has tendencies to behave that way, so allowing racial prolifing would only make it much worse. We all remember the recent incident in New York City, when a man was shot dead on his wedding day for no real reason, with over 10 bullets.