What Chance Of Innocence Can Be Tolerated For Conviction?

[Siegmund]

The instructions from the court tend to be something a bit vague, and my answer will float a bit based on the severity of the situation.

For a traffic-ticket appeal, I am happy with 5/100, and could probably tolerate ten.

For a misdemeanor something less than 1/100 is ok - if I had to cite a specific one-size-fits-all number I'd probably pick something close to 1/100. For something like a murder trial I would be very nervous if there was as much as 1 in 1000 chance of being wrong.

There's a tradeoff between how many guilty people are let off the hook and how many innocent ones are jailed. People, especially classical statisticians, are prone to always fixing the risk of Type I error.

A better approach might be to compare the relative severities of being wrong in each direction, and find the spot on a power curve that matches that. In the case of the traffic fine, both types of error are more or less trivial; in the case of a murder, I would judge condemning an innocent man to be something like 100 times worse than freeing a guilty one--- and my equilibrium point would be something like accepting a 10% chance of freeing a guilty man in exchange for a 1/1000 chance of condeming an innocent one.

[Archon_Wing]

To all:

How would the degree of punishment affect you, eg (prison, death)? I would think the reversibility of a wrong conviction should matter too.

[Taraz]

I think a better question is how do you convert each piece of evidence into some kind of probability that the defendant is guilty? How can you calculate how sure you are?

[chezlaw]

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To all:

How would the degree of punishment affect you, eg (prison, death)? I would think the reversibility of a wrong conviction should matter too.

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makes a huge difference. Reversability of a wrong aquital would matter as well.

but everthing makes a difference e.g. the stupider the law the higher degree of certainty required, 101% in some cases.

chez

[PairTheBoard]

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I see what your saying but you could make an attempt to figure out its mathematical value on average:

The first attempt to quantify reasonable doubt was made by Simon in 1970. In the attempt, she presented a trial to groups of students. Half of the students decided the guilt or innocence of the defendant. The other half recorded their perceived likelihood, given as a percentage, that the defendant committed the crime. She then matched the highest likelihoods of guilt with the guilty verdicts and the lowest likelihoods of guilt with the innocent verdicts. From this, she gauged that the cutoff for reasonable doubt fell somewhere between the highest likelihood of guilt matched to an innocent verdict and the lowest likelihood of guilt matched to a guilty verdict. From these samples, Simon concluded that the standard was between .70 and .74.

(interesting article- not definitive proof of anything- http://www.valpo.edu/mathcs/verum/pa...oubtFinal.pdf)

[/ QUOTE ]

I think what it shows is that people will pick Probability Numbers if they are forced to. That doesn't mean it's a good idea to force them to do so. It also doesn't mean using those numbers in an artificial idealized probability model is a good idea. The conclusions manufactured by that model may very well be far inferior to the Best Judgement of the jurors deliberating on the evidence normally.

PairTheBoard

[Siegmund]

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[ QUOTE ]
To all:

How would the degree of punishment affect you, eg (prison, death)? I would think the reversibility of a wrong conviction should matter too.

[/ QUOTE ]
makes a huge difference. Reversability of a wrong aquital would matter as well.


[/ QUOTE ]

Well, yeah.

Welcome to real life: the damage done by either error is completely irreparable. It's illegal to try someone for the same crime twice, and impossible to award someone extra years of life to make up for the ones he missed out on. You can take a wrong conviction off someone's record, and you can hand him some money - but this does absolutely nothing for repairing his reputation or undoing what he went through during the trial and time imprisoned.

Yes, you waste more years of someone's life by executing him than you do by locking him up awhile and then freeing him -- but that's a difference of amount of damage done, not a matter of one being reversible.

[chezlaw]

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[ QUOTE ]
To all:

How would the degree of punishment affect you, eg (prison, death)? I would think the reversibility of a wrong conviction should matter too.

[/ QUOTE ]
makes a huge difference. Reversability of a wrong aquital would matter as well.


[/ QUOTE ]

Well, yeah.

Welcome to real life: the damage done by either error is completely irreparable. It's illegal to try someone for the same crime twice, and impossible to award someone extra years of life to make up for the ones he missed out on. You can take a wrong conviction off someone's record, and you can hand him some money - but this does absolutely nothing for repairing his reputation or undoing what he went through during the trial and time imprisoned.

Yes, you waste more years of someone's life by executing him than you do by locking him up awhile and then freeing him -- but that's a difference of amount of damage done, not a matter of one being reversible.

[/ QUOTE ]
I'm not sure it is illegal in the uk to try someone again if further evidence comes to light. Not sure but they were certainly talking about allowing it. Also they can retry on similar charges. Edit: yep its allowed

The rest just seems wrong. I'd be more likely to convict if there was a decent appeals procedure and a competent agency was looking for more evidence. Its not about giving them back the years lost but reducing the downside of being wrong.

chez

[Piers]

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What Chance Of Innocence Can Be Tolerated For Conviction?

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I'll go with whatever society decides. As long as it is not too much out of whack it’s not important.

The important thing is that society, as a whole does not loose confidence in the legal system.

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is it acceptable that they come to different verdicts not because they disagree on chance of innocence but because they disagree on what that chance need be for an acquittal.

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They will do it any way, so might as well accept it.

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The definition of "chance of innocence in your mind" is how many out of one hundred cases with identical evidence would the defendent actually be innocent

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I do not have a default definition, I’m happy to go along with anyone else’s.

[David Sklansky]

First of all I disagree with those who say that there is a problem with using numbers. If you use my definition, "the number of people out of 100 who IN YOUR OPINION would actually be innocent given the exact same evidence (including even things like demeanor on the witness stand), I believe that most people could comprehend that.

Secondly I vehemently disagree with chezlaw. If we did start putting a number on chances of guilt in whodonit cases, what possible reason is there not to specify what those chances should be in a juror's mind for various crimes? In chezlaws's scenario you could have a hung jury because eleven voted to convict each of whom thought the chances of innocence was 2% while another voted to acquit thinking there was only a one percent chance of innocence. Because he thought one percent was enough. Even worse would be the jury that should be "hung", but isn't, because the one jury member who thinks there is a 25% chance of innocence doesn't believe that he should vote to acquit.

To not specify a number threshold adds an element of luck to the verdict that shouldn't be there.

As far as what that number should be, I think it depends on the crime, the punishment faced, and other circumstances. And I'm not sure who should do the specifying, the judge, the legislature whatever. And again it only applies to purely whodonit cases.

I realize the logistics of this is daunting if not impossible. But at the very least it should be undersood that in least in theory, this is the best solution. For those who would object that it makes the process too mathematical, I would remind you again that the probability assessment is still an individual personal opinion. But there is no reason why that personal opinion can't be put in a form that is more precise than the words "reasonable doubt".

[David Sklansky]

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I think a better question is how do you convert each piece of evidence into some kind of probability that the defendant is guilty? How can you calculate how sure you are?

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There is a nice tool that usually works well. Especially if the pieces of evidence are unrelated. (In other words if you find out the murderer is over three hundred pinds like the defendent, and then find out the murderer is over six three like the defendent its different than if you later found out they are both redheads.) But I won't utter the name of that tool here.