But notice that these are examples of restrictions on evidence of guilt. The assumption (very reasonable, it seems to me) is that human irrationality tends in the direction of false positives, i.e. wrongful convictions. (Possibly along with the assumption that our values require a lower tolerance for false positives than false negatives.)
If juries are capable of convicting on the sort of evidence presented at the Knox/Sollecito trial (and they are, whether in Italy, the U.S., or anywhere else)...well, can you imagine all the false convictions we would have if such rules as you listed were relaxed?
The bias toward false positives is probably especially strong in criminal cases. The archetypal criminal offense is such that it unambiguously happened (not quite like the Willingham case), and in the ancestral human environment there were far fewer people around who could have done it. That makes the priors for everyone higher, which means that for whatever level of probability you’re asking for it takes less additional evidence to get there. That a person is acting strangely might well be enough—especially since you’d have enough familiarity with that person to establish a valid baseline, which doesn’t and can’t happen in any modern trial system.
Now add in the effects of other cognitive biases: we tend to magnify the importance of evidence against people we don’t like and excessively discount evidence against people we do. That’s strictly noise when dealing with modern criminal defendants, but ancestral humans actually knew the people in question, and had better reason for liking or disliking them. That might count as weak evidence by itself, and a perfect Bayesian would count it while also giving due consideration to the other evidence. But these weren’t just suspects, but your personal allies or rivals. Misweighing evidence could be a convenient way of strengthening your position in the tribe, and having a cognitive bias let you do that in all good conscience. We can’t just turn that off when we’re dealing with strangers, especially when the media creates a bogus familiarity.
But notice that these are examples of restrictions on evidence of guilt.
No, they’re not. The first one I listed can go either way.
“Since my client is a woman, you should reduce the odds you assign to her having committed a murder by a factor of 4.”
The second one can go either way too; it just as much excludes e.g. hearsay evidence that implicates someone else.
The assumption (very reasonable, it seems to me) is that human irrationality tends in the direction of false positives, i.e. wrongful convictions.
Sure, but that needs to be accounted for via the guilt probability threshold, not by reducing the accuracy of the evidence. Favoring acquittal through a high burden and biasing evidence in favor of the defendant is “double-dipping”.
If juries are capable of convicting on the sort of evidence presented at the Knox/Sollecito trial (and they are, whether in Italy, the U.S., or anywhere else)...well, can you imagine all the false convictions we would have if such rules as you listed were relaxed?
I only listed a few examples off the top of my head. The appropriate comparison is to the general policy of, per Bayesianism, incorporating all informative evidence. This would probably lead to more accurate assessments of guilt. In particularly egregious cases like K/S, it would have been a tremendous boon to them to allow them to have an explicit guilt threshold and count up the (log) likelihood ratio of all the evidence.
In any case, remember that there’s a cost to false negatives as well. Although that’s heavily muddled by the fundamental injustice of so many laws for which such a cost is non-existent.
Let me take a step back here, because despite the fact that it sounds like we’re arguing, I find myself in total agreement with other comments of yours in this thread, in particular your description of how trials should work; I could scarcely have said it better myself.
Here’s what I claim: the rules of evidence constitute crude attempts to impose some degree of rationality on jurors and prosecutors who are otherwise not particularly inclined to be rational. These hacks are not always successful, and occasionally even backfire; and they would not be necessary or useful for Bayesian juries who could be counted on to evaluate evidence properly. However, removing such rules without improving the rationality of jurors would be a disaster.
(Let’s not forget, after all, that there were people here on LW who reacted with indignation at my dismissal of certain discredited evidence in the Knox case, protesting that legal rules of admissibility don’t apply to Bayesian calculations—as if I had been trying to pass off some kind of legal loophole as a Bayesian argument. Such people were apparently taking it for granted that this evidence was significant, which suggests to me that it is very difficult for people—even aspiring rationalists—to discount information they come across. This provides support for the necessity of rules that exclude certain kinds of information from courtrooms, given the population currently doing the judging.)
Okay, then I think we’re in agreement. I guess I had interpreted your earlier comment as a much stronger claim about the mapping between pure Bayesianism and existing legal systems, but I definitely agree with what you’ve said here. I would just note that it would probably be more accurate to say that the rules of evidence are hacks to approximate Bayes and correct for predictable cognitive biases, though perhaps in this context those aren’t quite separate categories.
I think that is an incomplete description of the justification of the rules of evidence—some of these rules are also introduced to discourage particular abuses of the system, such as unreasonable searches. Otherwise, agreed.
But notice that these are examples of restrictions on evidence of guilt. The assumption (very reasonable, it seems to me) is that human irrationality tends in the direction of false positives, i.e. wrongful convictions. (Possibly along with the assumption that our values require a lower tolerance for false positives than false negatives.)
If juries are capable of convicting on the sort of evidence presented at the Knox/Sollecito trial (and they are, whether in Italy, the U.S., or anywhere else)...well, can you imagine all the false convictions we would have if such rules as you listed were relaxed?
The bias toward false positives is probably especially strong in criminal cases. The archetypal criminal offense is such that it unambiguously happened (not quite like the Willingham case), and in the ancestral human environment there were far fewer people around who could have done it. That makes the priors for everyone higher, which means that for whatever level of probability you’re asking for it takes less additional evidence to get there. That a person is acting strangely might well be enough—especially since you’d have enough familiarity with that person to establish a valid baseline, which doesn’t and can’t happen in any modern trial system.
Now add in the effects of other cognitive biases: we tend to magnify the importance of evidence against people we don’t like and excessively discount evidence against people we do. That’s strictly noise when dealing with modern criminal defendants, but ancestral humans actually knew the people in question, and had better reason for liking or disliking them. That might count as weak evidence by itself, and a perfect Bayesian would count it while also giving due consideration to the other evidence. But these weren’t just suspects, but your personal allies or rivals. Misweighing evidence could be a convenient way of strengthening your position in the tribe, and having a cognitive bias let you do that in all good conscience. We can’t just turn that off when we’re dealing with strangers, especially when the media creates a bogus familiarity.
No, they’re not. The first one I listed can go either way.
The second one can go either way too; it just as much excludes e.g. hearsay evidence that implicates someone else.
Sure, but that needs to be accounted for via the guilt probability threshold, not by reducing the accuracy of the evidence. Favoring acquittal through a high burden and biasing evidence in favor of the defendant is “double-dipping”.
I only listed a few examples off the top of my head. The appropriate comparison is to the general policy of, per Bayesianism, incorporating all informative evidence. This would probably lead to more accurate assessments of guilt. In particularly egregious cases like K/S, it would have been a tremendous boon to them to allow them to have an explicit guilt threshold and count up the (log) likelihood ratio of all the evidence.
In any case, remember that there’s a cost to false negatives as well. Although that’s heavily muddled by the fundamental injustice of so many laws for which such a cost is non-existent.
Let me take a step back here, because despite the fact that it sounds like we’re arguing, I find myself in total agreement with other comments of yours in this thread, in particular your description of how trials should work; I could scarcely have said it better myself.
Here’s what I claim: the rules of evidence constitute crude attempts to impose some degree of rationality on jurors and prosecutors who are otherwise not particularly inclined to be rational. These hacks are not always successful, and occasionally even backfire; and they would not be necessary or useful for Bayesian juries who could be counted on to evaluate evidence properly. However, removing such rules without improving the rationality of jurors would be a disaster.
(Let’s not forget, after all, that there were people here on LW who reacted with indignation at my dismissal of certain discredited evidence in the Knox case, protesting that legal rules of admissibility don’t apply to Bayesian calculations—as if I had been trying to pass off some kind of legal loophole as a Bayesian argument. Such people were apparently taking it for granted that this evidence was significant, which suggests to me that it is very difficult for people—even aspiring rationalists—to discount information they come across. This provides support for the necessity of rules that exclude certain kinds of information from courtrooms, given the population currently doing the judging.)
Okay, then I think we’re in agreement. I guess I had interpreted your earlier comment as a much stronger claim about the mapping between pure Bayesianism and existing legal systems, but I definitely agree with what you’ve said here. I would just note that it would probably be more accurate to say that the rules of evidence are hacks to approximate Bayes and correct for predictable cognitive biases, though perhaps in this context those aren’t quite separate categories.
I think that is an incomplete description of the justification of the rules of evidence—some of these rules are also introduced to discourage particular abuses of the system, such as unreasonable searches. Otherwise, agreed.