treis, by the way, interesting question. Meant to add that above.
I agree with your objections and I suppose I should have included that stuff in the scenario. However I do believe that I (luckily) specified that the study was of murder cases and the father was the murderer in 99% of the cases.
Ah yes I see your point now. However is there not some nonzero chance that the persons DNA, fingerprints or whatever were not involved in the crime? Aren’t we making an underlying assumption that when those things are found there is a very high probability that the person they belong to is the guilty party? This is an assumption that we can make becuase the case history and logic in most cases come agree with that assumption. Why doesn’t the study in this case establish that the assumption of the father being the murderer is correct?
In other words if we have a body and trace the DNA of the fetus back to John Doe and using assumptions justified by the survey to try him how does that differ from finding his DNA in her vagina and tracing it back to him?
And here I was thinking it was dangerious minorities!
(I aplogize for continually adding information to the scenario I guess I needed to be more clear. Thank you for your kind words ** Campion **)
I think you need to face up to the limitations of your hypothetical situation. Perhaps you make too much of the concept that someone was convicted “by DNA.” Evidence of DNA in the vagina only puts the suspect on the scene. It does not establish guilt. Correct me if I am wrong, but you seem to have this idea that, Perry Mason style, a prosecuter can just whip out DNA test results and the trial is over. DNA does not prove rape. If a woman claims I raped her, and my defense is there was no intercourse, then a DNA test can show me to be a liar, which would weaken my defense. If my defense is the sex was consensual, then DNA alone will not convict me. Other evidence must be presented. So the existence of a positive DNA test or fingerprint match, in and of itself, is not enough to establish guilt.
Proving that someone is the father of a dead child, and presenting sociological evidence (remember, this type of evidence only predicts, it does not identify) that 99 times out 100 in such cases the father is the murderer, *in and of itself * is insufficient to convict anyone.
Yes it does appear that my hypothetical is lacking some very important pieces of information. I didn’t provide any evidence that a murder occured nor did the prosecutor prove it. I neglected that facet of the case and the legal beagles rightly set me straight.
No but I guess I am assuming things that I explicitly need to state. I am more focused on who committed a crime and less concerned with proving that a crime actually occured. In the rape case I should have added that there were obvious signs that the victim was forced into sex and then murdered and the prosecutor had proven this to the satisfaction of the jury.
Yes I do see that now. How about for instance the woman was found chopped up and stuffed into a barrell. Clearly this is was not an accident and by attempting to conceal the body whomever murdered her knew that they had committed a crime. Now we can agree that this new evidence would establish both that a murder occured and the murderer had a mens rea, correct?
Lets also assume that the prosecutor has successfully proved that the woman was pregnant, the defendant knew he was the father and they were estranged.
Now I believe that the necessary conditions have been satisfied that both a murder occured and the scenario satisifies the requirements for the study to apply. Is that study enough to find the defendent guilty of the crime?
Anyone remember, “Court Martial,” an episode of Star Trek: The Original Series? Captain Kirk stands trial on charges of negligence. The only direct evidence was the ship’s computer. No one questioned the accuracy of the logs because computers are infallible, yet no one thought the computer could have been sabotaged and the logs changed.
Shall we use statistics and probability to convict people just because the accused happened to be in a particular statistical category? I think not.
I am having a hard time making my point and I blame it all on my inability to make it clearly. I was hoping someone more eloquent would come along and help me out, but failing that…
It boils down to this. DNA testing excludes possible suspects, sociological studies (which in this excample is tantamount to profiling) includes them. You know the old Sherlock Holmes saying, “Whenever you haved ruled out the possible, whatever remains, no matter how improbable, is the answer”? What DNA testing attempts to do is rule out everybody but the suspect. That is where the “99%” figure comes in, although it is usually more like “99.52103%”. The prosecutor will say something like “Only one in 50 million men could have committed this crime. And that, along with everything else I have shown you, leads to the conclusion that X is guilty.” Proof beyond a reasonable doubt.
A sociological study, no matter how well done, is simply putting people in categories (inclusion) Depending upon how well it is done it can have predictive power, but not about individuals, only about groups. It has the potential to be evidence, I suppose, but it is not the kind of thing that offers proof.
Proof is obtained by ruling things out. Sociological studies cannot, by their nature, do that.
Ah Contrapuntal I think I have it!
Why is it that the DNA evidence excludes possible suspects? Its becuase we have assumed that the person’s semen in a woman’s vagina and the blood under her finger nails is the rapist. If they do not find my semen in her does that definitively mean that I am not the rapist? Certainly not, there is a small but non-zero chance that she had engaged in consensual albeit rough sex with a person and then I raped her with a condom on. However we have assumed that absent of other evidence that the person’s DNA that matches the blood and the semen is the rapist beyond a reasonable doubt.
The study that is presented in the OP is not evidence of the murder rather it is the justification for the assumptions the jury should make. The evidence in this case would be that the women is young, pregnant and estranged from her boyfriend. We then go to our study and start checking off boxes just as the jury does in a rape case and determine the verdict. Basically the jury does something like that for each case. In the rape example it would be:
Evidence of non-consual sex: Check
DNA of blood under finger nails matches the defendent: Check
DNA of semen matches the defendent: Check
Evidence meets assumptions necessary for proof beyond a reasonable doubt: Check
Verdict: Guilty
Using the study:
Evidence of a murder: Check
Victim is relatively young: Check
Victim is pregnant: Check
Victim and boyfriend are estranged: Check
Boyfriend knew he was the father: Check
Evidence meets assumptions necessary for proof beyond a reasonable doubt: Check
Verdict: Guilty
Basically all this study does is replace the logic and experience justification for a guilty assumption and replaces it with a systematic justification for a specific condition.
I certainly hope you are joking here. This should never be enough to convict someone of a crime.
He should be wringing his sweaty little hands, too.
Do I convict? No.
If you were hypothetically in charge of a fire station, would you refuse to hire women because they’re statistically unlikely to have the necessary strength? The law says no. There are always exceptions, and if that’s important when making hiring decisions, IMO it’s a million times as important during a trial.
Sure and the defense had a chance to offer those exceptions but chose not to.
No, he needs to have the evil gene, the one shared by Hitler and Walt Disney.
I would not convict. People should be judged as individuals, not as members of a specific group. In fact, I think that if a prosecutor did bring up evidence like this, it would be cause for a mistrial, in that he was deliberately poisoning the well and trying to turn jury sentiment against the defendant, instead of bringing out the facts.
I absolutely would not. Using that type of logic, you could argue that Blacks and Hispanics are more likely to commit crimes and on that basis the defendent should be found guilty.
The onus isn’t on the defense to prove that the defendant is an exception; the prosecution’s argument is invalid from square one simply because we know exceptions exist, which means there’s always reasonable doubt if the only evidence they offer is a statistic.
To continue my analogy, a female applicant at the fire station shouldn’t have to prove her strength any more than a man would, therefore a defendant who’s part of a suspicious group shouldn’t have to prove his innocence any more than someone in another group would.
The wikipedia link that Sentient Meat posted is terrific, and it explains why you can’t say 99% of these cases turn out to be the father, so it’s 99% likely that this time it’s the father.
The presumption of innocence requires that the odds of an individual being the perpetrator cannot be considered to be 1:1. Therefore, applying 0.99 to one and coming up with a 99% likelihood is a logocal fallacy. A URL=http://en.wikipedia.org/wiki/Prosecutor’s_fallacy]Prosecutor’s Fallacy, in fact (in case you didn’t catch it the first time).
Absolutely not. A sociological study is good enough to convince the police to look at someone as a suspect and gather evidence, but nowhere near enough to convict someone of a crime.
What of my assumption rationale?
If what you are trying to do is prove something, you cannot replace logic with anything. Without logic there is no proof. This, I believe, is where you are making your mistake. As others have suggested, read SentientMeats’s link again, as well as Campions’s post. The former shows why the assumption of guilt based on your “99%” study is a fallacy; the latter shows why the case would never even come to trial. The jury would never hear about the study. It is evidence of nothing at all. You need to understand this. Introducing a study about what thousands of other men have done tells you exactly zero about what I have done. There is no group of men who are identical in every way. You could find hundreds of identical traits that would include me in a particular group; there would still be thousands more traits that would exclude me.
Trials are about evidence.
I think the legal case has been addressed above (and I know I wouldn’t want to be convicted on a purely statistical argument), but read John Allen Paulos’ book **Innumeracy, where he discusses a trial in which a statistical argument was used in an attempt to convict. Fortunately, it was blown out of the water by a more savvy defense, with a better grasp of mathematics:
I went to Generic State U, and i remember that guy. Called himself a “Sociology Professor”, but he kept spelling Sociology with two "L’'s and falling asleep in class. I wouldn’t believe a word that came out of his mouth, him and his beady eyes, always wringing his hands and such…
When statistics are outlawed, only 99% of outlaws will have statistics.