> his DNA sample was on record after he had willingly given it to them as part of an investigation into a burglary at his mother's home some years earlier.
This is a worrying snippet. Many people in the UK think that DNA databases should include every citizen. There are often local campaigns of "have your DNA taken, get ruled off our suspect list" when there are murders or multiple rapes.
The police have pushed to include as many DNA profiles as possible.
They don't realise that false positives happen.
Keeping a DNA database of just the criminals means that you don't have to store information from 60 million people (approx current UK population), nor process unneeded data to find matches, nor worry so much about false positives.
The good human rights stuff drops out as a result of good data practices.
> [The police] don't realise that false positives happen.
Rather, they don't care. Neither do the prosecutors. They don't want to imprison innocents, but they also have a strong incentive to look the other way. That's why, for example, prosecutors fight hard to block initial DNA tests on those already imprisoned. (In the US anyway.)
Indeed. I've recently had an issue along those lines albeit on a lesser scale as a witness. The police were more interested in securing a good case for the CPS than actually fairly evaluating the situation. I was actually advised that my statement should only refer to the facts which were likely to aid a conviction rather than be a fair and balanced account of what happened. The moment a conviction was not obviously going to happen, they recommended that I withdraw my statement before they submit the case to the CPS.
I wrote an addendum sheet for the statement instead stating that they'd asked me to do that. That didn't go down well so I better move to another area if I want any policing or assistance in the future...
For ref, no-one was hurt other than insurance companies in this case. Two idiots bounced a car off each other at 20mph - neither need prosecuting.
Just to clarify. This isn't a false positive in the sense that the DNA test is flawed. The guy's DNA was transferred to the crime scene because he has a skin disorder which causes excessive flaking. But it can happen to anyone.
Every test has a false positive rate and if you scrutinize close enough you can often guess reasons/justifications for those false positives. These rationalizations really aren't so important though--- the crucial bit is understanding that there will always be false positives and making a reasonable estimate for how often they'll occur.
The odds of coming up positive on a DNA test are a lot higher than I would have originally believed:
"DNA matching for criminal cases looks at only a few specific loci and the alleles associated with them, so the chances of two separate people matching come in somewhere around 1 in 7,000"
http://www.fluther.com/145318/is-there-a-possibility-that-th...
I speculate, but "mass hysteria" seems to fit. "These are gruesome crimes; I have nothing to hide; I want to help the police; this is something I can do".
There are a few crimes in the UK that get a lot of press coverage, and I can imagine people living locally feel influenced by that.
England (and Wales, I guess?) has a huge DNA database, something like 4.5 million samples. These are taken from a few volunteers; and from people arrested for crime. If those people are not charged, or if they are charged and acquitted, the DNA sample is still retained. A recent trial in EU meant that we had to put some limits in - we keep innocent people's DNA for 6 years now.
There is a weird disconnect between many English people and privacy intrusions from the state. Lots of people were fine with the idea of a national ID card, and only turned against it when details of cost came out.
DNA testing and forensics in general is a complete scam. Most of it has already been proven to be pseudoscience or else is on its way to being proven so. And of the stuff that actually is at least potentially legit, like DNA testing, virtually all of the labs in the US are so poorly run that their results wouldn't even be admissible as evidence, let alone considered reliable, if more people actually knew what was going on there. If I remember correctly the last time the US government did an audit of its accredited forensics labs every single one failed, and the vast majority aren't even accredited to begin with.
>DNA testing and forensics in general is a complete scam
What? Every single one of those links either supports DNA testing or doesn't mention it.
It's certainly true that a lot of forensics turns out to be borderline pseudoscience or superstition (everyone should read the newyorker link when they have time) but don't just lump everything together.
(Also don't lead with a link to alternet unless you want bias readers against you!)
"Every single one of those links either supports DNA testing or doesn't mention it."
Did you read the NYT article?
Also, the issue isn't whether DNA testing could work in theory if it were done by academics under ideal conditions. The issue is whether or not the DNA testing that's actually done by forensics labs is A) accurate (not contaminated, read properly, etc.) B) used correctly by the courts. It also assumes that the police aren't planting evidence against suspects, either purposely or accidentally, that the chain of custody is maintained, etc. There is very little reason to think that these things are always the case.
The whole premise of the article is that if the DNA matches, the prosecutors argue that you're guilty, and if the DNA doesn't match, the prosecutors argue that you're guilty anyway. If the results of a forensic 'test' show that you're guilty no matter what the outcome, that's pretty much the very definition of a sham. They might as well be using a truth-telling chicken.
> His DNA sample was on record after he had willingly given it to them as part of an investigation into a burglary at his mother's home some years earlier.
Lesson to everybody: Don't ever voluntarily give your fingerprints or DNA. Once they get into the government databases, you can (a) never retract them (and nor can you change your fingerprints or DNA), and (b) you can fall victim to false matches.
Here's a similar case of a false match -- in this case for fingerprints:
Portland-area lawyer Brandon Mayfield was arrested in May 2004 because his fingerprint matched one found on a bag of detonators near the train station in Madrid in the March 11 2004 bombing, which killed 191 people. But Spanish authorities said the fingerprints belonged to another man, an Algerian. A US federal court later threw out the case against Mayfield, and the FBI expressed regret for the "fingerprint-identification error". As a former Army officer, Mayfield's fingerprints would be on file with the government. A law enforcement official said the fingerprints were not on file because of any crime or as part of the government's terrorism databases.
Forensics is not my field, but genetics is. Restriction enzyme digestion and gel electrophoresis seems to be the technique that is still being used for forensic DNA matching.
To my mind, it would make a lot more sense to simply genotype a few hundred well-chosen (highly variable) SNPs on a standardized array. Since there are premade arrays that give you tens to hundreds of thousands of SNPs for a few hundred dollars, you should easily be able to unambiguously identify a single individual even if (non-monozygotic twin) family members are in the haystack.
Obviously this says nothing about guilt, but from the DNA matching perspective we can and should do better.
I imagine it depends on the lab. A friend worked as an assistant at a place that did forensic dna matching five years ago and she definitely used your suggested method.
No, they do PCR amplification of highly variable STR sites and then measure the PCR products by capillary electrophoresis. The false positive match probability is low, unless partial matches are allowed.
It is of course very unfortunate that this man had to spend 8 months in jail. There was no lab error in this case (the man was a cab driver with a rare skin flaking condition and his skin flakes stuck to the nail polish of a passenger who was later the victim of murder). But of course errors do happen, someone in this thread quotes a 1% to 2% error rate for DNA testing.
Buit to put it in context, according to the Innocence Project, in 25% of the cases when DNA testing is used by the FBI during the investigation, it results in the suspect being exonerated. That 25% is a large number of innocent people who would be charged and tried and a lot of them would be convicted if not for the existence of DNA testing.
A basic understanding of statistics is sufficient to understand how this happens. Authorities have become obsessed with the idea of assembling giant DNA databanks of entire populations and then doing "cold hits" for unsolved crimes against the entire database.
The problem with this is that DNA testing is not 100% accurate, and when you test an entire population you're going to start getting false positives. The larger the population, the more false positives.
But then a jury may be told "there was a 100% DNA match" or that "There is a less than 1 in a billion chance that he is not the killer." And the wrong guy goes to prison.
Check out this other recent cold hit case. They took DNA samples from Occupy Wall Street protesters and then ran them against unsolved crimes files with no connection to the protesters just to see what they could get.
So a protestor is arrested and charged for a 2004 murder based on this. Later found to be an error, but getting to that point assumes you can afford a good lawyer. There are lots of people getting charged for unsolved crimes they have no connection to. Not all of them can afford a lawyer and expert witnesses.
New York recently passed a law requiring DNA samples from all persons convicted of any crime, even misdemeanors such as loitering.
There is a nationwide push for mass DNA collections. Other jurisdictions are pushing to take DNA of people who are merely arrested, regardless of whether there is a later conviction.
> South Carolina’s law enforcement agency will soon collect DNA samples from people when they’re arrested for a felony – rather than post-conviction – four years after legislators passed a law requiring the state’s DNA database to expand.
This push to states even comes from the federal level:
> Every day innocent people needlessly become victims of violent crimes. Most of these are committed by repeat offenders. By passing state legislation that enables law enforcement to collect DNA from felony arrestees, at the same time as fingerprints, your state can catch criminals sooner
There you can see that 26 states now mandate collection on arrest. More than half of the 50 states.
Supreme Court Chief Justice John Roberts has ruled that DNA sampling on arrest, regardless of conviction, is permissible:
> Since the mid-1990s, the USA and the United Kingdom have maintained databases that use a series of such alleles to match DNA from unsolved crimes to known or suspected offenders. In the USA, states and the federal government keep DNA indexes of suspects and unsolved crimes, and share information through a computer system maintained by the FBI.
"Guilt by the Numbers: How fuzzy is the math that makes DNA evidence look so compelling to jurors?" by Edward Humes was an article that covered the problems here pretty well.
Doing blind searches of samples on large DNA databases in order to find cold hits gives you a very high probability of a false match. A match that the falsely accused defendant will be quite difficult to challenge since there is a general belief by the public that DNA matches on a few markers are irrefutable proof of identity.
DNA can more strongly connect a suspect who is already known through other information. Doing blind searches isn't science and it isn't justice.
> For instance, if a DNA test capable of distinguishing between 'unrelated' people with one million to one confidence was used to create a database of two million personal profiles from a population of 20 million potential suspects you could be pretty certain that most crime stain profiles run against it would produce at least one cold hit.
> You could also be more than 90% certain that it would be the wrong cold hit. You could further expect that around 80% of the personal profiles on the database would match at least one other on record from a different person.
> Problems like these had led the 1996 National Research Council publication "The Evaluation of Forensic Evidence" (NRC-II) to recommend that "When the suspect is found by a search of a DNA database, the random match probability should be multiplied by N, the number of persons in the database".
On one side we have an argument that there are severe statistical problems with this. On the other side we have those who claim that is false and that the chance of any DNA match being wrong are so small as to be virtually impossible. Yet every year the number of false accusations and convictions from cold hits grows, as we see in this latest case.
It's maddening how badly almost everyone sucks at understanding and interpreting statistics (including many who have had significant training in doing so), and chilling when that is combined with a forensic method that is at heart statistical.
OJ Simpson got away with murder because the jury didn't understand statistics, and now more and more innocent people go to jail because juries and judges don't understand statistics.
The error rate of fingerprints is at least in the single digit %, but everything else is double-digits. Moreover, while DNA is theoretically extremely reliable, the error rate of DNa testing is dominated by lab error and is on the order of 1-2%. Yet, juries are generally not told this overall error rate, but rather just the theoretical probability of a false match (1 in trillions).
Attacking the reliability of DNA evidence can make you seem desperate. Of course they still need to do exactly that, but you are not just combating what the prosecution said (or failed to say) but what the jurors already "know". They "know" DNA is perfect magic evidence that gets the badguy every time on CSI.
In the UK some high profile cases indicated a lack of understanding of essential statistics on the part of many in the legal fraternity. Judges in summation often unwittingly misrepresented probabilities, or allowed tenuous statistical assertions to be left unchallenged in their instructions.
This was not unobserved by statisticians, and some effort had been made to redress this situation.
I was quite surprised when reading "The Drunkards Walk" when he talked about DNA evidence. The rates of false matches is really quite low (like one in tens of million chance if memory holds) as long as there are no errors in the lab. But there are. In fact, the odds of an error on the lab are on the order of one in 200. And juries aren't allowed to be instructed on that.
Because the defense must first provide some evidence that a mistake was, or could have been made, in order for the jury to receive such an instruction.
> Because the defense must first provide some evidence that a mistake was, or could have been made ...
No, they only need to describe the statistical probability of an error -- they don't need to uncover specific evidence that an error was made in a particular case. And they can empanel expert witnesses to describe the kinds of errors that are typical of the method, but again, without having to uncover evidence unique to the present case.
> Presumably that's beyond the reach of a defendant on legal aid.
Yep. Some might call that a defect in our legal system (that fair representation is out of reach of indigent defendants). Others, cynics all, might assert that if you can't pay for the justice, don't do the crime.
> No, they only need to describe the statistical probability of an error
I can see that comprehension is not your strong suit. As I said, they must show that a mistake was, or could have been made.
You can show that a mistake could have been made by showing the statistical probability of an error. Generally, this statistical evidence must be sufficiently specific as to apply to the circumstances of the matter at hand.
> I can see that comprehension is not your strong suit.
Here is what you said: "Because the defense must first provide some evidence that a mistake was, or could have been made"
It's false, I corrected you. A statistical probability of a false positive is not evidence that a mistake was, or could have been, made. It is a statistical prediction for a particular outcome, and it's not a mistake -- the practitioner is assumed to be performing the procedures as specified, and is blameless.
If I say that, given the usual distribution of population IQs (mean 100, SD 15), that 4.78% of the population will have an IQ at or above 125, is that a mistake? Will someone be brought up on charges of negligence?
Actually, it is. Contrary to your claim, a statistical outlier, a false positive, is not called a "mistake" and no one is brought up on charges. The legal term is typically "Act of God" or another similar term.
> And in all fairness, when dealing with the law, what is "legal" trumps what is "logical."
The lede paragraph in this interesting article raises the key question:
"Scientists, lawyers and politicians have raised new concerns over the quality of forensic evidence testing - so is the criminal justice system too reliant on lab tests without realising their limitations?"
I'm grateful for some of the specialized publications on a skeptical worldview, such as Skeptic magazine and Skeptical Inquirer magazine and some of the websites and books recommended in those magazines, for teaching over the last decade or more that even "scientific" approaches to questions that come up in court cases have often never been validated. I was surprised to discover that even the old technique of matching fingerprints is still the subject of a lot of recent scholarly studies
and that there is NOT full validation of all the techniques that have long been used to show fingerprint matches between criminal case suspects and fingerprint impressions found at a crime scene. The article submitted here makes the important point even the latest gee-whiz technology, DNA typing, which is usually the key to solving crimes on television drama shows, has significant limitations. Sometimes DNA samples are poorly gathered, and sometimes DNA test results are ambiguous.
It takes a combination of multiple lines of evidence that are consistent with one another best to prove guilt beyond a reasonable doubt. Lawyers for criminal defendants do the right thing when they argue vigorously over every factual basis for the state's claim that an accused defendant is guilty. I was an appellate clerk once upon a time for a state supreme court that reviewed all first-degree murder convictions in the state. I had to read a lot of case files with gory crime scene photographs and lots of transcripts of witness testimony to events and expert witness testimony about the findings of scientific tests. Sometimes a case is supported by so many lines of evidence that no reasonable appellate judge could doubt the sufficiency of the evidence shown at trial. Other times a conviction at trial is reversed on appeal not because of factual innocence, but because of legal errors by the prosecution. But every once in a while, even after a conviction at trial under the standard of presuming innocence beyond a reasonable doubt, a very reasonable doubt that wasn't considered fully at trial is preserved in the court record and forms the basis of reversing the trial court judgment on appeal. No one line of evidence is foolproof, not even DNA.
sounds like someone couldn't read a gel electrophoresis ? How long did they run the gel for ? Accuracy can be increased in a read with a longer gel ... Were they using some 4" gel ? There are tons of variables. And as stated in the article some of them aren't even running the right tests.
It's worse than that. As the article points out, we shed cells everywhere, and the possibility exists that the test was conducted fairly and accurately, but it doesn't prove what the prosecutor claimed -- that the DNA proved guilt. All the DNA proved was that the defendant's DNA was present where the measurement took place, but this doesn't necessarily mean the defendant was ever there, or was present at time time of the crime.
It also alludes to the separation of concerns in forensic examinations creating a new set of problems. For example, the DNA testers had a sample to test, and little to no knowledge of the greater context.
On the other hand without separation of concerns, you get the risk of the lab "finding" what the investigators wanted, like the incidents in the FBI labs in the 1990s.
This is a worrying snippet. Many people in the UK think that DNA databases should include every citizen. There are often local campaigns of "have your DNA taken, get ruled off our suspect list" when there are murders or multiple rapes.
The police have pushed to include as many DNA profiles as possible.
They don't realise that false positives happen.
Keeping a DNA database of just the criminals means that you don't have to store information from 60 million people (approx current UK population), nor process unneeded data to find matches, nor worry so much about false positives.
The good human rights stuff drops out as a result of good data practices.