Back To The Shoe Argument

[David Sklansky]

I need to resurrect it with all this mathematical wrangling going on about evidence. I forget what people's original answers were.

Suppose a man is on trial for murder and the jury is on the verge of acquitting him in spite of their strong suspicion of guilt because the evidence leaves room for reasonable doubt. But at the last minute a footprint is uncovered at the murder scene. It is definitely the murderer's. And it is the same size as the defendent. If it wasn't, its instant acquittal. But since it is the jury is now contemplating a conviction.

Do you agree or not that the rarer the shoe size, the greater the reason for the jury to convict?

[Taraz]

I would agree that the likelihood of guilt would be higher, but not necessarily high enough that they should convict. It would depend on so many other factors.

[Lestat]

It seems to me that the rarer the shoe size, the greater the likelihood that it belongs to the accused. Therefore, if only 1% of the population has a EEEE shoe, a EEEE shoe print was found at the murder scene, the defendant is a possible suspect to have been at the murder scene, AND... The defendant has a EEEE shoe size.... If I'm on the jury, I say it is more likely for this shoe print to belong to the nurderer (since you stated it's definitely the murderer's shoe print), than any other random person with a EEEE shoe.

[samsonite2100]

I don't see how anyone could disagree with this.

[Siegmund]

"Do you agree or not that the rarer the shoe size, the greater the reason for the jury to convict?"

As long as you mean that the footprint was presented as evidence late in the prosecution's case, and as long as you aren't asking me to specify how rare it has to be to make the doubt too small to be reasonable - then yes.

If you literally mean that the footprint is discovered while the jury is deliberating, then, no, the footprint wasn't part of the evidence presented, and the jury isn't told of its discovery until after the acquittal.

[yukoncpa]

If it’s already a boarder line situation, but there is a little room for reasonable doubt, then new evidence finds that the defendant and murderer wear a size 15 shoe, he is now guilty beyond a reasonable doubt.

[David Sklansky]

The first two responses are exhibiting some kind of math phobia or mental block. This is very disconcerting so I am going to try to show in precise detail why this guy deserves to be convicted.

Firstly lets say that the jury originally believed that there was a 20% chance he was innocent. What precisely do I mean by that? It means that the jury thinks that if they were presented with a million identical cases with the exact same evidence, 200,000 of the defendents would be innocent. First make sure you understand that definition.

OK, now assume that the shoe size fits one percent of the population. Now lets go back to the million identical defendents. 800,000 are guilty. All 800,000 have that shoe size. 200,000 are innocent. 2,000 have that shoe size. The other 198,000 are sent home. The trial now is for 802,000 defendents. All identical with the (adjusted) exact same evidence. Now the jury believes that one quarter of one percent of the defendents are innocent. (2000 out of 802,000).

Bringing it down to one defendent, the shoe evidence should change the juries probability of innocence from 20% to one fourth of one percent. The fact that juries may not think that way is neither here nor there.

[mjkidd]

A small but pertinent hijack: Reasonable doubt is generally defined as:

"Any doubt which would make a reasonable person hesitate in the most important of his or her affairs."

Given this standard, what is the probability of innocence at which you would be comfortable convicting someone?

[Taraz]

[ QUOTE ]
The first two responses are exhibiting some kind of math phobia or mental block. This is very disconcerting so I am going to try to show in precise detail why this guy deserves to be convicted.

Firstly lets say that the jury originally believed that there was a 20% chance he was innocent. What precisely do I mean by that? It means that the jury thinks that if they were presented with a million identical cases with the exact same evidence, 200,000 of the defendents would be innocent. First make sure you understand that definition.

OK, now assume that the shoe size fits one percent of the population. Now lets go back to the million identical defendents. 800,000 are guilty. All 800,000 have that shoe size. 200,000 are innocent. 2,000 have that shoe size. The other 198,000 are sent home. The trial now is for 802,000 defendents. All identical with the (adjusted) exact same evidence. Now the jury believes that one quarter of one percent of the defendents are innocent. (2000 out of 802,000).

Bringing it down to one defendent, the shoe evidence should change the juries probability of innocence from 20% to one fourth of one percent. The fact that juries may not think that way is neither here nor there.

Bringing it

[/ QUOTE ]

I would agree with you, but I don't think you can break down someone's probable guilt that clearly. For me it would depend on why I had reasonable doubt. Clearly the shoe-print evidence is huge, I think it would just depend on the particulars of the case.

For example, if the defendant admitted to being at the crime scene, the shoe-print is practically irrelevant. That's why I said it depends on so many other factors.

(Edit: Somehow I missed it when you said the following [ QUOTE ]
If it wasn't, its instant acquittal. But since it is the jury is now contemplating a conviction.

[/ QUOTE ] I guess I would agree with you in that case, but I still maintain that it would clearly depend on many factors.)

[Piers]

The American legal system is beyond me, however the rarer the shoe size the more likely the accused is to be the murderer.