# Statistics say he did it, Do you convict? **URL:** \ **Category:** Great Debates\ **Created:** [June 6, 2005, 2:36pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132 "2005-06-06T14:36:20Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [June 6, 2005, 2:36pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/1 "2005-06-06T14:36:20Z")
Lets say that you are a hypothetical juror hearing a murder case. The victim in question is a 24 year old, pregnant, recently estranged from her boyfriend that is the father of the child. No body was found nor was there any eyewitness or physical evidence that links the father to the murder. None the less he has been arrested and is now on trial for the crime. Lets also assume that there was a way for the father to easily have disposed of the body, say he owns a fishing boat that can travel far out onto a large lake they live on. During the trial the prosecuter calls his one and only witness, a professor of Sociology from Generic State University. This professor has dedicated his career to studying the circumstances that surround murders. In this case he has done a meticulous study and found that in cases in which the victim is recently estranged from the father, young and pregnant the father is the murderer in 99% (or which ever number constitutes beyond a reasonable doubt to you) of the cases. The study in question is tight and the conclusions and application in the case is sound. Lets say that this is the only evidence entered in the case and the defense basically argued that the prosecuter has not proven anything. Is the study enough evidence for you to find the defendant guilty beyond a reasonable doubt? To me I am very much on the fence about this case. Looking at it objectively assuming the study is sound there doesn’t seem to be any reasonable doubt that he is the murderer. Why would fingerprints with a same level of confidence as the study be proof but the survey not? Both things point to the father with the same level of accuracy. However there just seems to be something wrong about using the study becuase it doesn’t really show anything other than the fact that a lot of guys in the same situation have killed their ex-girlfriends. It seems wrong that a man is convicted on the sole basis of what others in a similar situation has done. Thoughts? ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [June 6, 2005, 2:54pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/2 "2005-06-06T14:54:41Z")
[No](http://en.wikipedia.org/wiki/Prosecutor%27s_fallacy). ---
**Author:** ![Driver8](https://avatars.discourse-cdn.com/v4/letter/d/b5a626/32.png) [@Driver8](https://boards.straightdope.com/u/Driver8)\ **Post date:** [June 6, 2005, 2:58pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/3 "2005-06-06T14:58:47Z")
I’d say there is plenty of reasonable doubt. I would not convict. I guess if the study has the same reliability as fingerprint or DNA sampling my conclusion makes little sense. But I think I would find it really hard to swallow that the study was as concrete as physical evidence. One could not say there is no reasonable doubt that someone else could have done it in the absense of any physical evidence, no matter what the statistics say. ---
**Author:** ![Larry\_Borgia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/larry_borgia/32/156_2.png) [@Larry\_Borgia](https://boards.straightdope.com/u/Larry_Borgia)\ **Post date:** [June 6, 2005, 3:04pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/4 "2005-06-06T15:04:48Z")
Besides **SentientMeat’s** mathematical reasoning, there is a moral element to this. When we here evidence of a case we expect to hear evidence linking the specific person to the crime. With fingerprints the evidence says "These fingerprints are 99.9999% likely to be Joe Jones’. " With Sociological reasoning the evidence says “Murders like these are 99.9999% likely to be committed by people like Joe Jones.” The first case ties the suspect specifically to the crime, the other puts the suspect in a class of people who were likely to commit the crime. A court should judge individuals, not classes. I’m sure it would not be hard to imagine cases where the hypothetical sociological reasoning could be grossly misused by the state. Especially since I don’t think sociological reasoning is anywhere near as accurate IRL as in this hypothetical. ---
**Author:** ![Larry\_Borgia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/larry_borgia/32/156_2.png) [@Larry\_Borgia](https://boards.straightdope.com/u/Larry_Borgia)\ **Post date:** [June 6, 2005, 3:06pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/5 "2005-06-06T15:06:23Z")
:smack: when we **hear** evidence, that is… I keep doing stuff like this… ---
**Author:** ![Campion](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@Campion](https://boards.straightdope.com/u/Campion)\ **Post date:** [June 6, 2005, 3:23pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/6 "2005-06-06T15:23:27Z")
It doesn’t matter what I think I would do; as a juror, I would never get the case. The prosecutor’s study fails to establish the elements of the crime; having failed to make a prima facie case that _this_ defendant committed _this_ crime, the judge must dismiss the case. ---
**Author:** ![Larry\_Borgia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/larry_borgia/32/156_2.png) [@Larry\_Borgia](https://boards.straightdope.com/u/Larry_Borgia)\ **Post date:** [June 6, 2005, 3:27pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/7 "2005-06-06T15:27:06Z")
> [@Campion](#): > > It doesn’t matter what I think I would do; as a juror, I would never get the case. The prosecutor’s study fails to establish the elements of the crime; having failed to make a prima facie case that _this_ defendant committed _this_ crime, the judge must dismiss the case. You are correct, **Campion**. But I think what the OP is looking for is the underlying flaw in the reasoning in his (?) hypothetical, not what an actual court would do if a prosecutor actually brought this forward with no more evidence than in the OP. ---
**Author:** ![Bricker](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@Bricker](https://boards.straightdope.com/u/Bricker)\ **Post date:** [June 6, 2005, 3:30pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/8 "2005-06-06T15:30:54Z")
As a juror, I would vote to acquit, because the prosecution failed to establish each and every element of the crime beyond a reasonable doubt. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [June 6, 2005, 3:57pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/9 "2005-06-06T15:57:10Z")
> [@treis](#): > > Thoughts? I think your hypothetical is outside the realm of possibility, and so is not meaningful in any way. It’s like saying: what if it were discovered that 99.99% of all people with red hair have committed murder. Should we arrest all red headed people? Nature does not work that way, so you have postulated an alternate universe in which case alternate legal rules would apply. ---
**Author:** ![Jonathan\_Chance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jonathan_chance/32/701_2.png) [@Jonathan\_Chance](https://boards.straightdope.com/u/Jonathan_Chance)\ **Post date:** [June 6, 2005, 4:05pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/10 "2005-06-06T16:05:19Z")
Hell, the underlying flaw I see is that while all killers of this type are fathers etc not all fathers etc and killers. Acquit. You’re going to have to show me some specific evidence that this person was involved before I MIGHT be willing to take such evidence into account. But maybe not. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [June 6, 2005, 4:50pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/11 "2005-06-06T16:50:35Z")
Well, I wouldn’t, but some jury’s might. After all they convicted Scott peterson with not much more evidence than that. (The evidence agains him was primarily:“1 It was a really heinous crime 2. He was lying scum 3. His alibi wasn’t much good and 4. Did I mention it was a _really_ heinous crime?” :rolleyes: ) ---
**Author:** ![Paul\_in\_Qatar](https://avatars.discourse-cdn.com/v4/letter/p/ccd318/32.png) [@Paul\_in\_Qatar](https://boards.straightdope.com/u/Paul_in_Qatar)\ **Post date:** [June 6, 2005, 4:51pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/12 "2005-06-06T16:51:32Z")
No. The State has not proved a crime was committed. The State has not connected this person with this act. The State has not established Motive, Opportunity and Ability. The defendant has no case to answer for. Deliberate to ten in the morning to get the per diem then go home. ---
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [June 6, 2005, 5:09pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/13 "2005-06-06T17:09:50Z")
> [@Larry Borgia](#): > > With fingerprints the evidence says "These fingerprints are 99.9999% likely to be Joe Jones’. " With Sociological reasoning the evidence says “Murders like these are 99.9999% likely to be committed by people like Joe Jones.” The first case ties the suspect specifically to the crime, the other puts the suspect in a class of people who were likely to commit the crime. A court should judge individuals, not classes. I’m sure it would not be hard to imagine cases where the hypothetical sociological reasoning could be grossly misused by the state. Especially since I don’t think sociological reasoning is anywhere near as accurate IRL as in this hypothetical. Sure studies are not this accurate in real life but hey thats the beauty of hypotheticals ;). I see your point about classes of people but I am not sure it applies in this situation. The study in this case does link a specific person to the crime namely the father of the baby. I guess I don’t see the difference between saying the finger prints pointing 99% accurately to Joe Jones and the study (given the conditions are met) showing that Joe Jones (assuming he is the ex) to 99% accuracy. > [@Campion](#): > > It doesn’t matter what I think I would do; as a juror, I would never get the case. The prosecutor’s study fails to establish the elements of the crime; having failed to make a prima facie case that this defendant committed this crime, the judge must dismiss the case. Why doesn’t the study count as prima facie evidence that the father of the child is the murderer? > [@John Mace](#): > > I think your hypothetical is outside the realm of possibility, and so is not meaningful in any way. It’s like saying: what if it were discovered that 99.99% of all people with red hair have committed murder. Should we arrest all red headed people? Nature does not work that way, so you have postulated an alternate universe in which case alternate legal rules would apply. Yes the scenario postulated in the OP is most likely beyond the realm of possibility but given enough specifics you can get a fairly high likelyhood. I think we ought to agree on the idealized case before we move to any real life situation. > [@Jonathon Chance](#): > > Acquit. You’re going to have to show me some specific evidence that this person was involved before I MIGHT be willing to take such evidence into account. Why is this any less specific than say matching DNA found in a rape victim to a suspect. Basically my line of reasonin is: Premise: The murderer in cases like this one has a probability of 99% of being the father Premise: The suspect is the father Conclusion: The suspect has a 99% probability of being the murderer How does that differ from: Premise: The rapist in cases like these has a probability of 99% of being the person whos sperm is found in the victim Premise: The suspect’s sperm was found in the victim Conclusion: The suspect has a 99% probability of being the rapist. Replace 99% with the necessary number that satisifies beyond a reasonable doubt. > [@Bricker](#): > > As a juror, I would vote to acquit, because the prosecution failed to establish each and every element of the crime beyond a reasonable doubt. Is this becuase no body was found? If so then go ahead and assume that a body was found. I merely said it wasn’t in the OP becuase I wanted to consider only the evidence of the study and wanted to exclude evidence possibly given by the body. > [@Paul in Saudi](#): > > No. The State has not proved a crime was committed. Ok, assume also that the prosecuter also proved that the victim was indeed murdered. > [@Paul in Saudi](#): > > The State has not connected this person with this act. Sure it has by way of the study. > [@Paul in Saudi](#): > > The State has not established Motive, Opportunity and Ability. I wasn’t aware that it necessarily had to do any of the above. Of course by proving that the defendent is guilty the prosecuter proves that there necessarily must have been the opportunity and the ability to committ the crime. ---
**Author:** ![Contrapuntal](https://avatars.discourse-cdn.com/v4/letter/c/e274bd/32.png) [@Contrapuntal](https://boards.straightdope.com/u/Contrapuntal)\ **Post date:** [June 6, 2005, 5:16pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/14 "2005-06-06T17:16:14Z")
> [@treis](#): > > I see your point about classes of people but I am not sure it applies in this situation. The study in this case does link a specific person to the crime namely the father of the baby. I guess I don’t see the difference between saying the finger prints pointing 99% accurately to Joe Jones and the study (given the conditions are met) showing that Joe Jones (assuming he is the ex) to 99% accuracy. I see at least two problems. First, you are assumning that sociology and biology are equivalent disciplines; they aren’t. Second, testing one person to see if he fits into a group of one is very different from testing a group of people to see who fits in it. ---
**Author:** ![vetbridge](https://avatars.discourse-cdn.com/v4/letter/v/b5e925/32.png) [@vetbridge](https://boards.straightdope.com/u/vetbridge)\ **Post date:** [June 6, 2005, 5:18pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/15 "2005-06-06T17:18:24Z")
Not enough information in the OP to come to a conclusion. Does the defendant have beady, little eyes that dart back and forth? That’s what we need to know. ---
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [June 6, 2005, 5:26pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/16 "2005-06-06T17:26:25Z")
> [@Contrapuntal](#): > > I see at least two problems. First, you are assumning that sociology and biology are equivalent disciplines; they aren’t. That is true but this is an idealized case. Obviously no study can get that sort of accuracy and there is no way a prosecutor would end his case there. I guess the fundamental question underlying all of this is how much weight, if any, should we give to studies like this. > [@Contrapuntal](#): > > Second, testing one person to see if he fits into a group of one is very different from testing a group of people to see who fits in it. I don’t think I fully understand this objection. > [@vetbridge](#): > > Not enough information in the OP to come to a conclusion. > > Does the defendant have beady, little eyes that dart back and forth? That’s what we need to know. Unfortunately for the defendent he lost both eyes in a freak chalupa accident. I don’t know if you can consider his glass eyes to be beady but they sure aren’t darting back and forth 😉 ---
**Author:** ![Campion](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@Campion](https://boards.straightdope.com/u/Campion)\ **Post date:** [June 6, 2005, 5:37pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/17 "2005-06-06T17:37:49Z")
> [@Larry Borgia](#): > > You are correct, Campion. But I think what the OP is looking for is the underlying flaw in the reasoning in his (?) hypothetical, not what an actual court would do if a prosecutor actually brought this forward with no more evidence than in the OP. Ok. My issue was partly that there was no evidence to prove up fundamental elements of the crime: no evidence that the defendant knew the woman, that she was pregnant, that he was the father, that she disappeared, that he had the requisite mens rea, etc. But focusing on flaws in the study alone: as has been said before, and better, the study does does not show that _this_ man committed a crime, just that men who are in some respects like him have committed similar crimes to the one he is accused of. (That sentence should be taken out and shot, but I’ll leave that to others to do.) > [@treis](#): > > Why doesn’t the study count as prima facie evidence that the father of the child is the murderer? A prima facie case is one in which all the elements of the crime are proven. Whether they can be rebutted by the defense is a separate, and for purposes of this argument, irrelevant issue. But if the prosecutor cannot make a prima facie case (meeting all elements), then it doesn’t matter what the study says. You would need, at a minimum, two witnesses other than the study’s author: the ob-gyn (who would need to testify that she was pregnant and the defendant was the father); and the cop (who would need to testify to death, cause of death, and the defendant’s opportunity). **Paul in Saudi** , motive is not actually an element of the crime, but you are correct that most prosecutors will try to prove motive because the jury wants to know why he did it. But back to the study: let’s assume you’ve proven those predicate facts about the defendant’s relationship to the victim and the baby, you’ve found the body, and the cop testifes that the defendant owns a boat that would permit him to go out on the water and dump a body. Here’s the primary problem: all murder statutes in the US require a specific mental state, what the law calls _mens rea_. That means that you must prove that the defendant _himself_ actually had a specific intent to cause the victim’s death. It isn’t enough to show that other men in similar situations had the mental state, you must show that this defendant did. Take a look at [California’s murder statute](http://caselaw.lp.findlaw.com/cacodes/pen/187%2D199.html): > [@Cal. Pen. Code sections 187 and 188](#): > > 1. (a) Murder is the unlawful killing of a human being . . . with malice aforethought. > > 2. Such malice may be express or implied. It is express when > there is manifested a deliberate intention unlawfully to take away > the life of a fellow creature. It is implied, when no considerable > provocation appears, or when the circumstances attending the killing > show an abandoned and malignant heart. > When it is shown that the killing resulted from the intentional > doing of an act with express or implied malice as defined above, no > other mental state need be shown to establish the mental state of > malice aforethought. Neither an awareness of the obligation to act > within the general body of laws regulating society nor acting despite > such awareness is included within the definition of malice. So the primary problem with the study is that it proves nothing about what this defendant actually did. That is why the study is not prima facie evidence that he killed her – the study says nothing about what this defendant did. (I would also move to exclude the study as more prejudicial than probative and as improper opinion. I think I might win on that first ground.) Is the study enough to convict the defendant in the court of public opinion? Yes. Would it stand up in a court of law? My opinion, no, not as the sole evidence of murder. ---
**Author:** ![Paul\_in\_Qatar](https://avatars.discourse-cdn.com/v4/letter/p/ccd318/32.png) [@Paul\_in\_Qatar](https://boards.straightdope.com/u/Paul_in_Qatar)\ **Post date:** [June 6, 2005, 5:37pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/18 "2005-06-06T17:37:58Z")
So you are saying she has beany eyes? (I know, no decent chalupa has beans, but still.) ---
**Author:** ![Contrapuntal](https://avatars.discourse-cdn.com/v4/letter/c/e274bd/32.png) [@Contrapuntal](https://boards.straightdope.com/u/Contrapuntal)\ **Post date:** [June 6, 2005, 5:42pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/19 "2005-06-06T17:42:50Z")
> [@treis](#): > > I don’t think I fully understand this objection. If one person has committed a crime than the set of \ contains one element, the criminal. DNA or fingerprint testing attempts to identify the criminal by eliminating every person who is not part of that set. That’s what the “99%” figure means. 99% of the population does not fit the profile (in this case, DNA ID or fingerprints.) Furthermore, the crime has already been committed. There is not a _predictive_ element in DNA testing. A sociological profile simply says that of all the cases studied involving A, the perpretrators were B 99% of the time. It _predicts_ that when the criminal is found, he wil be B. It says nothing about any particular individual, and it says nothing about any B’s who might not be the perpretrator. Your special case example where B could only be one person does nothing to change the method used to identify him, or the fact that it is a predictive one rather than a descriptive one. ---
**Author:** ![Annie-Xmas](https://avatars.discourse-cdn.com/v4/letter/a/ecc23a/32.png) [@Annie-Xmas](https://boards.straightdope.com/u/Annie-Xmas)\ **Post date:** [June 6, 2005, 5:45pm UTC](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132/20 "2005-06-06T17:45:17Z")
Statistics don’t murder people. People murder people. [Next page](https://boards.straightdope.com/t/statistics-say-he-did-it-do-you-convict/307132.md?page=2)