But are you sure the number is not just unacceptably high because [...] many of them would have to have been seen as having substantially greater than 13% chances of innocence? If not for some biasing effect like that, it's hard for me to see why the moral question would suddenly be clear once it was stated in population frequencies rather than in individual probabilities.
Well, people's intuitions about justice aren't all that consistent, so I don't think this particular moral question is going to suddenly become clear to all observers no matter how it's stated. That being said, though, I don't think we have any particular reason to think that Guede was convicted on unusually shaky evidence, so it seems reasonable -- given certain assumptions -- to take our estimates of his case as representative of murder cases in general.
A 13% innocence threshold for each particular case won't give you a 13% innocent prison population (assuming good estimates, which is probably generous in this context), but if we adopt that criterion and Guede's in the middle of the probability distribution for murder defendants, it seems likely that the resulting population-level incidence would still land on the bad side of 8 or 10%. Which doesn't look much better.
By the way, I should probably clarify that I don't think the LW average of 87% probability of guilt for Guede at all means that he should have been acquitted. I attribute the low number to a lack of confidence due to not having delved sufficiently deeply into the case, as per the third point in my earlier comment.
One should only believe that a miscarriage of justice has occurred in his case if one believes that the jury should not have had more than (say) 87% confidence. But in order to believe that one would presumably have to be highly confident in one's belief about what information the jury had.
Continuing my interest in tracking real-world predictions, I notice that the recent acquittal of Knox & Sollecito offers an interesting opportunity - specifically, many LessWrongers gave probabilities for guilt back in 2009 in komponisto’s 2 articles:
Both were interesting exercises, and it’s time to do a followup. Specifically, there are at least 3 new pieces of evidence to consider:
Point 2 particularly struck me (the press attributes much of the acquittal to the expert report, an acquittal I had not expected to succeed), but other people may find the other 2 points or unmentioned news more weighty.
2 Probabilities
I was curious how the consensus has changed, and so, in some spare time, I summoned all the Conscientiousness I could and compiled the following list of 54 entries based on those 2 articles’ comments (sometimes inferring specific probabilities and possibly missing probabilities given in hidden subthreads), where people listed probabilities for Knox’s guilt, Sollecito’s guilt, and Guede’s guilt:
It’s interesting how many people assign a high-probability to Knox being guilty; I had remembered LW as being a hive of Amanda fans, but either I’m succumbing to hindsight bias or people updated significantly after those articles. (For example, Eliezer says .15 is too high, but doesn’t seem otherwise especially convinced; and later one reads in Methods of Rationality that "[Hagrid] is the most blatantly innocent bystander to be convicted by the magical British legal system since Grindelwald's Confunding of Neville Chamberlain was pinned on Amanda Knox.")
EDIT: Jack graphed the probability against karma:
2.1 Outliers
If we look just at >41% (chosen to keep contacts manageable), we find 12 entries out of 54:
I have messaged each of them, asking them to comment here, describing if and how they have since updated, and any other thoughts they might have. (I have also messaged the first 12 commenters or so, chronologically, with <41% confidence in Knox’s guilt, with the same message.) The commenters:
AngryParsley / Cyan / Daniel_Burfoot / Eliezer_Yudkowsky / GreenRoot / John_Maxwell_IV / LauraABJ / Mario / Matt_Simpson / Morendil / Psychohistorian / Shalmanese / Threads / Unknowns / badger / bentarm / bgrah449 / bigjeff5 / brazil84 / dilaudid / jimmy / kodos96 / lordweiner27 / mattnewport / nerzhin / tut
I look forward to seeing their retrospectives, or indeed, anyone's retrospectives on the matter.