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Science

Are Fingerprints Unique? 119

MattJ writes "There's an incredible article in LinguaFranca about fingerprints. Maybe they're not all unique after all. And maybe those fingerprint experts are not much more scientific than handwriting experts. Fascinating details."
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Are Fingerprints Unique?

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  • Maybe O.J. was innocent....
  • If they fingerprints fit, maybe we'll acquit.

  • haha..
    very funny..
  • by account_deleted ( 4530225 ) on Saturday November 18, 2000 @04:56AM (#615861)
    Comment removed based on user account deletion
  • I seem to recall reading somewhere (probably New Scientist) that fingerprints were made as the result of a more limited things, rather like the wat you can pull random numbers of a seed number.

  • This could mean many more convicted criminals are not really guilty? Oh the lawyers will have fun with this one! They are already trying to get people out of prision, but now they have even better evidence. This could end up costing the court system lots of money to retry thousands of cases, most of which probably shouldn't be retried.
  • What can I say? I've seen them all and man they're all the same.

    Sorry.

    Dan
  • kinda like Bush and Gore...
  • better that 1000 innocent people be convicted rather than 1 guilty person go free
  • Facsinating details, but nothing conclusive.
  • by ka9dgx ( 72702 ) on Saturday November 18, 2000 @05:27AM (#615868) Homepage Journal
    It's time to push for someone to do the math, some experiments, and determine the actual error rates, factors, etc. I can't believe there is NO possiblity of an error in a "match". There has to be a false-positive as well as a much higher false-negative rate, we need to know what they are, so we, as a society, do the right thing, instead of the emotionally appealing expedient.

    To guestimate, I suspect the real numbers are about 10^12:1 false matches, which is quite alarming, if there are 10^7 entries, one in 10,000 will be a false hit with someone totally at random. The false negative rate is probably closer to 1% and might be as high as 10%.

    Does anyone have better numbers, after all, I'm just guessing at this point.

    --Mike--

  • The article goes on about how the assumption that no two prints are identical haven't been proven. This is of cource rather obvious, this statement cannot be proven, it can only be strengthened by failing to falsify it.

    There is never any proof that is 100% watertight (other than in mathematics and other formal logic systems). The legal system will always have to settle for reasonable proof.

    If an investigator picks up a suspect and his prints happen to match the perps, then you will have a hard time to prove you didn't do it. But remember it must also be proven that the prints that were found are indeed the criminals.

    It's wery unlikly in my view that the fingerprint matching is ever the weakest link in the chain of evidence.
  • by Tebriel ( 192168 ) on Saturday November 18, 2000 @05:31AM (#615870)
    Puddin' Head Wilson was wrong. Bad Mark Twain!
  • by Anonymous Coward
    No O.J. was clearly guilty. On the other hand, there was lots of proof that the cops planted evidence at both crime scenes. It would have been wrong to convict O.J. on planted evidence. Crooked cops are far worse than one murderer.
  • by CakerX ( 149266 ) on Saturday November 18, 2000 @05:40AM (#615872)
    Well fingerprints although not unique as we once though still provide good evidence. I remeber reading somewere that about 1 in 10,000 people have similar fingerprints. they still would be crucial evidence if the over 100 people with the same fingerprints in the country never set foot in the city.
  • by the real jeezus ( 246969 ) on Saturday November 18, 2000 @05:43AM (#615873)
    ever since the mid-1980s, when Automated Fingerprint Identification Systems (AFIS) began to emerge...

    Great. We're trusting a multi-variable analytical computer system that's as old as Pac Man... Especially considering that:
    The strongly held belief among FPEs that latent fingerprints can be matched to one person alone, wrote David Stoney in a 1997 legal practice manual, is "the product of probabilistic intuitions widely shared among fingerprint examiners, not of scientific research."

    and
    ...proficiency tests reveal high rates of error by FPEs.

    I could just picture the conversation in the lab at Lockheed International Conglomerate:
    "Richard, I've been thinking...what about distortion from pressure on either the latent print or the test print, or both!" "Oh Sam, you know we only have 640KB of RAM to do our matrix multiplications in...and besides, the government's paying us a lot for this. We're gonna have one hell of a Christmas bonus..."

    Consider this, too:
    But forensic fingerprint identification is supposed to compare two different impressions from the same finger. As Stoney noted, "No two things, no two representations of this person's signature, no two representations of their fingerprint will be exactly alike." The test, therefore, ought to have used two different impressions from the same finger to establish a baseline score for a match. "It is really shocking," Stoney testified, "to see something presented...that doesn't have that basic element of forensic examination in part of the study."

    Great, they may as well be dowsing for water wells now... Okay, I bet $10 that the feebs' [fbi.gov] computer (AFIS) is a total fraud. The burden of proof, however, is on you...

    This sucks. I'm going back to bed.



    In 1999, marijuana [smokedot.org] killed 0 Americans...
  • There is never any proof that is 100% watertight

    Oh yeah? Prove it, smart boy!
  • by Jonathan ( 5011 ) on Saturday November 18, 2000 @05:49AM (#615875) Homepage
    The software is available (in every police station), the data is available (also in the police stations) -- let's just see what the percentage of cases where the programs claim that the figureprints of two different people are the same.
  • The question is not whether fingerprints are globally unique -- as the article points out, given enough detail, they most certainly are, like all natural things.

    The question is whether any two fingerprints differ enough for a smudged, low-detail, partial impression of a fingerprint to reliably match the one and not the other.

    That is where the science ends and the craftsmanship begins.

  • For instance, at my work we use an Iris scanner to get into the building. That isn't useful for forensics, but for access to restricted areas........ Just imagine if you had finger prints almost the exact same as someone who had unrestricted (fingerprint) access to Nuclear Weapons. Bit of a strech, but it could happen.

    Now, I'm not sure just what the accuracy is in the scanner, but let's assume for a moment that it's the same as "1 in 10000" that's being tossed around for fingerprints in this discussion.

    At the same time, assume that the pattern of someone's Iris and their finger prints aren't linked in any way.

    Combine the 2 and you've got a 1 in 10 billion chance of having duplicate records.

    Dark Nexus
  • You are missing the point. Such tests have been performed, just scan the article for "50K vs. 50K".

    The point is not whether fingerprints are unique -- the point is how many fingerprints match any particular (low-detail, smudged, partial) impression of a fingerprint.

  • , it can only be strengthened by failing to falsify it.

    Failing to falsify does not strengthen an argument. For example, prove that Unicorns don't exist. Nothing you can present will prove that they don't exist, therefor they must exist!
  • Uh.... if i take your assumption of 1 in 10,000 people having similiar fingerprints, lets start assuming...

    a) That's 7,322,564 people in New York,NY (1990 US Census) with a rate of 1/10,000 gives approx. 732 similiar ones give or take a variance of 1/x^2, whatever x being. Maybe as many as 1000, as few as 500.

    b) That's further assuming we discount all the transient workers coming into town & all the tourists. Which may double the population on a given day. A population doubling due to this would not just double the "similiar score" to 1464, but would be something on the order of, hmm... 732^2, or 535824. Wow.. half a million, because this is combinitorial. Suzie Q182 matches 1464 other fingers, and each of those 1464 other fingers have thier own set of 1464 matches, but not with 100% overlap. False positives tend to blow up.

    In fact, you could prove that someone out there has two fingers that are similiar to another persons singular digit. I'm not sure how to finagle the numbers to find out if the two fingers would be rated as similiar or dissimiliar. There probly is a secondary rate preventing a person from having two matching fingers.

    Now for some more fun, you give the assumption that "if the over 100 people with the same fingerprints in the country never set foot in the city" to determine what country your talking about. (all figures are Bistro-Math(tm), please don't nitpick, instead create your own cosmology)

    100 people times 10,000 is 1 million plus a bit for the guy with the finger that lives in the town. Well, you don't live in Albania(3,490,435) ,Liechtenstein(32,207), or Bangladesh(129,194,224). But you may be referring to Botswana(1,576,470), or Estonia(1,431,471), or Swaziland(1,083,289). Or go to http://www.infoplease.com/ipa/A0004389.html to find out for yourself.

    Basically, a rate of 1/10,000 is scientifically un exceptable. And since there is no "rate" since all mistakes are due to technician error, not error in the system (can you say Cult?) there is no way for it to be a science.

  • ...look up the April 1999 issue, crypto fans. It contains an article about "The Voynich MS", a book (we THINK it's a medical textbook) from the Renaissance that NO ONE has been able to decypher. Solve this one, and you'll have one doozy of a line in your resume (and maybe, we'll find out something really neat in medicine!) Oh, yes, the illustrations are way-kewl, too: wild flowers, Terry Gilliam-style plumbing, and LOTS of naked women. The translation project has been on the net since 1991, and is WAY underpublicized, so I'm throwing this in to help out. Good Hunting!
  • Damn, my fingerprints aren't unique, my ideas aren't unique... at least my Slashdot nickname [slashdot.org] is completely unique.

    Phew, I feel better!

  • The point of the arguement is that Finger Printing as it now stands can never be conclusive. It currently falls into the pseudo-science realm with astrology, dowsing, and advertising. In such that; if you do it wrong, you must not be doing it right. That the lack of falsifiability (ouch) is what raises science above the snake-oil, ponzi-schemes and Presidential Elections. It is equally interesting about the dogmatic zeal which FPEs defend thier core tenants. Perhaps more proof that: cognitive ideas = k, and that we are only redistributing them to reach the least entropic state. Kinda like a society wide protien fold of group thought. Better folding = more prosperous society, etc. Hows that for psuedo-science?

  • Comment removed based on user account deletion
  • by Anonymous Coward
    but nothing conclusive.

    But that's the point. There isn't anything conclusive one way or the other.

    Please keep in mind the principle of "Innocent until proven guilty."

    What procecutors are doing is asking juries to convict people soley on the basis of fingerprints which may not be a valid identification technique.

    So what's actually being said is "He might be the owner of the fingerprints, but we can't be certain. Heck, we don't even know if you can identify people by fingerprints!" Do you really think someone should be convicted of a crime on that basis?

    Oh ... and to those people out there who are thinking: "Well, we know he's a criminal; we just need the fingerprint match so we can lock him away." Why even bother with evidence? You've already made up your mind that he's guilty, you don't need the fingerprint matches to show that. What you should really be doing is lobbying congress to revoke all this nasty trial business (since all the criminals can get off on technicalities) and implement a system whereby we just simply lock away people we know are criminals.

  • He did not say the FBI center, he said local LEO.
    In many states, you get printed each time you are arrested.
    Just by using an old set vs a new set for one suspect, you could then get a "Z" reference to other prints.

    Since I have been printed 4 times in the last 5 years ( Professional Certffication and background checks) , I can tell you that the TX DPS has different imprints on my fingerprints and that they do differ. My girlfriend's prints are slowly disappearing, she's an EPA lab chemist. That in itself generates a "Z" factor. So there is a basis to run a true comparison test to determine the APIS DB's accuracy in matches.


  • Two dead people are far worse than acquitting on technicalities.
  • Yeah, and it's a shame LA didn't _prosecute_ the crooked cops, but just let them retire to Idaho.

    A cop who lies in court should lose his pension. A cop who falsifies evidence should go to prison.

  • The attempt to prove that a non-existant creature does not exist is what is known as an unfalsifiable statement. There is no possible way to prove that a non-existent being does not exist.

    The correct approach in science and in philosophy is to start with a falsifiable statement (such as "Unicorns exist"). The more scientists and philosophers search for evidence of the existence of unicorns and fail, the more likely it becomes that unicorns do not exist.

    have a day,

    -l

  • But low resolution data are exactly the data the tests should be run on, and at least from the article it sounds like such a test has never been done. The 50K vs. 50K test used high resolution prints (unlikely to be found at a crime scene), and was therefore flawed (as the article says).
  • by truefluke ( 91957 ) on Saturday November 18, 2000 @06:57AM (#615891) Homepage

    I needed to be fingerprinted before they would give me my green card, what fascinated me was this machine they took my fingerprints on.

    At first glance it looks like a photocopier gone haywire, with a largish monitor. This is where your fingerprint image gets projected. There are several squares of different sizes, and they look similar to the glass partition of an everyday photocopier.

    No ink involved, He just asked me to lightly place my fingers on the glass, and he held my fingers at some points to keep them from jiggling (he was very exacting about it).

    When he was satisfied, he brought the images of my prints up on the screen in front of us. He remarked "Well, no life of crime for you". He was referring to the fact that I had "excellent patterning". He remarked that "You have excellently defined fingertips" etc. etc. He then showed me the neatest thing he magnified my prints to the point that he could COUNT the skin pores between the whorls of my thumbprint

    Actually I was impressed, since up til that point it had always involved me getting my fingers full of that stupid ink and having to roll them around on a piece of paper. That machine was much cooler.

    And for the record, I don't have one :)

  • by ahertz ( 68721 ) <ahertz@yahoo.com> on Saturday November 18, 2000 @07:02AM (#615892)
    Folks, rememeber the OJ trial? There we saw DNA evidience, based on modern science, with proven error rates and a far lower possibility of subjective reading, being totally rejected as forensic evidence. And yet, many people are locked up every day on the basis of fingerprint evidence, based on 19th century science, with unproven error rates and based entirely on subjective judgement.

    Does anyone else see a double standard here? And how can we help society to make better, objective scientific judgements, rather than just listening to demagogues?
  • I remember taking a tour of the FBI headquarters in DC when I was a kid. They had a picture on the wall of two guys. One of whom had been mistakenly arrested for a crime the other (it turned out) had commited. They arrested him, because his fingerprints matched the ones at the crime scene. Turned out that the two men had identical fingerprints (or near enough).

    The nice people at the FBI made it sound like this was a 1 in a billion chance (which, technically, would make it so there are 6 other people out there with the same finger prints as me!), and that it was a freak thing. I'm inclined to agree with that.
  • by Anonymous Coward
    Two dead people are far worse than acquitting on technicalities.

    Yeah, 'cause we all know that if we had convicted OJ, it would have brought them back to life.

  • Will the police mention its SLIGHT problem to us?
  • Comment removed based on user account deletion
  • >The question is not whether fingerprints are globally unique -- as the article points out, given enough detail, they
    most certainly are, like all natural things.

    But when you scan them at a low enough resolution they all end up being the same. The trick is to adjust the resolution of the scan so the unique details show up.
  • This is yet another example of poor science© It has almost become the case that science means wearing a white lab coat while stating something as fact©

    This is causing significant backlash©

    The growth of psychic hotlines, faith healing and other panaceas is at least partly due to poor science© If the bar isn't held high enough that only science can qualify many other things can get through©

    Here in New Zealand there was a prominant case of a boy with cancer where the boy's parents rejected traditional therapy and went with some quantum vibration panacia© The boy died a couple of weeks ago© Many people are blaming the parents, but could they have any way of rating one over another© Both treatments were applied by people who said they would work©

    There have been many cases where medicine has shown use of poor science© There are diseases that people have fought for years to have the medical community investigate them, let alone accept their existance© Many people distrust doctors these days©

    This effect happens in other areas© People have commented that all the major advances in physics occur after the previous generation of physicists die out¥I can't claim to actually know that is true however

    Scientists' reputations are declining in this world© One day I would like to see Philosophy of Science taught early at school© When everybody is throwing information at you claiming they are facts© Everybody needs to be able to evaluate whether or not whether or not that information comes from a reliable method©

  • And I just found two identical snowflakes yesterday too!
  • We seem to entrust vital decisions in our lives to unvalidated, unscientific, suboptimal methods. Fingerprint identification methods apparently have never been statistically verified. Many of the voting machines and methods we use also lack scientific evaluations of their reliability and margin of error.

    As long as the people who fund voting machines and police labs don't understand what is necessary, the money for accurate scientific evaluations doesn't get allocated. And that comes ultimately down to scientific illiteracy.

    It's ironic that the guy who likely will have to fix this, George "W" Bush, and his staff (including Jams Baker) have displayed such a stunning lack of scientific literacy themselves by proclaiming, without evidence, that "machine counts are more reliable".


  • No two fingerprints the same? Weeeeell... let's not get carried away here.

    The (extremely valid) point here is not that fingerprinting isn't useful, but that it is by no means an infallible method. If you have a suspect and their prints could not POSSIBLY match the ones from the crime scene, then you can be pretty sure this isn't your man. However, to say that the main structure of the ridges of the two prints is exactly the same, that some of the secondary characteristics match, and that overall this is without a doubt a match.... that's kind of sketchy.

    Developmental biology is far from the nice, linear-type science the public seems to believe it is... Certain attributes of the organism at any stage of it's development can be approximated, but it's not always as simple as "gene X is present, so phenotype (trait) Y will be expressed". The future of the "designer baby" where parents could pick and choose their child's characteristics is far, far in the future (even then it wouldn't be exact). Why? Because... genes are like a set of very general rules... it's chaos theory at it's finest. Here is a system that obviously has some underlying order (to produce an organism with 2 eyes, antennae, whatever), but even barring gross mutation, prediction of the final results of an organism's development is still (at this point) an estimate, at best.

    It would be impossible to say exactly how many hairs a mouse would have, their precise location, and what color each would be by only looking at the genes of the creature. There's innumerable chances for deviation. You can stick two similarly colored mice together and say; "these mice are similar", but until you had an exact, infallible catalog of every minute detail of the organism, you would have no empirical (scientific) basis for saying how similar they are, or even "these mice are exactly alike". Even exactly the same genes (identical twins/clones) produce different results if you look closely enough.

    BUT... that's a far cry from an objective justification for the impossibility of 'lighting striking the same place twice';P. The same 'proof' was used when "they" once said that no two snowflakes are exactly alike. Whiiiich... after someone did some serious, scientific researcg on the matter, later turned out to be bullshit;). Much in the same vein, "the identical twins had different prints" argument means jack; two people could have different sets of genes in respect to their fingerprints, exist in different environments, and it's still not impossible that they would end up with extremely similar (or even indistinguishable) fingerprints. There's a quite a few people in the world; see "Europeans descended from 10 males" a few days back... even though America's a large place, those ancestors have passed on a little bit to everyone with caucasian ancestry - that's a lot of people with the same daddies/similar genes;). Is it that hard to imagine that, even though the odds are extremely small, that two sets of prints, taken right off the two specimen's fingers, could be similar to the point that they would appear exact?

    Now for the coup-de-gras... the fingerprints in crime scenes aren't lifted straight off someone's fingers in a controlled manner. There isn't some fingerprinting technician dipping the criminals fingers in grease and carefully applying them to the doorknob or whatever. As mentioned, smudging, processing, and method of extraction result in very loosely defined fingerprint specimens. Is it crazy to think that you can, 100% of the time, say with 100% certainty that "These fingerprints belong to this individual"? You bet. Should fingerprinting be forgotten, then? No, it's still useful, but... I think the courts have led people to believe that fingerprints are the end-all-be-all of forensic evidence. If America's going to claim that it's judicial system operates by "innocent 'till proven guitly", we might as well make the extra effort to make sure that the methods that we use to prove someone guilty are as sound as possible, or the system quickly becomes a farce.

  • This is not about what kind of detail is required to distinguish any two fingerprints -- it is about whether the impressions of fingerprints obtained from a crime scene (that is, smudged, partial, etcetera) can reveal such detail.
  • The likelyhood of Unicorns existing (or having existed) is not affected by lack of evidence. They either exist(ed) or don't(didn't) exist. It's all or nothing.
  • DNA fingerprinting?

  • That is all very interesting, but besides the point of the article, which questions the science behind the FPE's claim that any two impressions of a fingerprint can be reliably matched.

    The reason why this science is questioned is because the FPE's take overlapping, smudged, partial impressions, then rely primarily on their their experience and intuition to determine how great the likeness between the impression and the known fingerprint should be.

  • Failing to falsify does not strengthen an argument.
    That claim, although popular, is false. Failing to falsify does strengthen an argument; it merely can't prove it. It is possible to gather evidence for the non-existence of an object. There's even a whimsical statement of the paradox: "Every green blade of grass further convinces me that all crows are black."

    Here's how it works. The statement "All crows are black" is logically equivalent to the statement "All non-black objects are non-crows."
    So, assuming there's a finite universe of objects -- take that one up with the cosmologists -- I can estimate the probability that there exists a non-black object that is, in fact, a crow, simply by counting non-black objects, and looking to see crows among them. A good place to start is out on my lawn; I'll go through and see if any of the green objects sprouting from the soil out there is a crow.

    Nope: they're all weeds...I mean, blades of grass. That's still more evidence for the thesis that all crows are black.

    To carry this through to your thesis that there are no unicorns, the statement "There are no unicorns" is logically equivalent to "All objects are 'non-unicorns'". I can't acquire any evidence of the first one directly, but I can provide evidence of the second.
  • I still don't see what such a test would contribute.

    What the article questions is the science behind the method used by FPE's.

    According to the article, what happens is that FPE's get a (partial, smudged) fingerprint impression and rely on their experience and intuition to determine whether or not the amount of similarities found is sufficient for identification. When the FBI tells them what to look for, suddenly their judgment sways in the other direction.

    This has very little to do with the extent to which known fingerprint impressions match eachother.

  • Iff fingerprint matching is the only link in the chain, then fingerprint matching is the weakest link.

    Iff a stronger form of evidence is added to a chain containing only fingerprint matching, then fingerprint matching is the weakest link.

    Iff a stronger form of evidence is added to a chain containing fingerprint matching and any stronger evidence, then fingerprint matching is the weakest link.

  • Oops, forgot to point out, if fingerprinting is the weakest link in the chain, means that it is the strongest piece of evidence. This seemes to be missed in your post and the child posts. And since the acticle was predicated based apon a case where the fingerprint was the strongest piece of evidence, this counts against the "unlikelyness" of the even occuring.
  • Look a little closer at my post again...

    See? Up at the top there? The part where I said it isn't useful for forensics?

    People should learn how to read and pay a bit of attention before they try to learn how to make witty or sarcastic replies...

    Dark Nexus
  • by XNormal ( 8617 ) on Saturday November 18, 2000 @08:34AM (#615911) Homepage
    The first person to fashion a statistical foundation for this assumption was the British gentleman scientist Sir Francis Galton. He calculated the probability that any two fingerprints would resemble each other in all particulars as one in sixty-four billion.

    Even if you accept this figure of one in 64 billion the birthday paradox predicts that you can expect to find an identical pair of fingerprints in a database of sqrt(64e9) fingerprints which is just a little over 250,000. I believe the FBI fingerprint database is significantly larger than that. After this "threshold" of sqrt(N) is crossed the number of duplicates starts to rise quite sharply as the database size increases.


    ----
  • Iris scanners don't need a PIN as a hint or an index key to the database. There's apparently enough uniqueness, so you can compare the input with thousands of others and not get a false positive or negative.

    Whereas with all the fingerprint scanners I've seen you need a PIN or some other info, so that the computer knows which record to compare with the biometric input.

    This is for biometric access, not for forensic, but it should give you an idea on how relying 100% on partial fingerprint smudges really isn't a good idea.

    Cheerio,
    Link.
  • Did you forget to read the article? He never concludes that fingerprints can be the same instead he concludes with the judge disallowing testimony about the validity of fingerprinting's validity.
  • Or worse yet 999 innocent people convicted and the 1 guilty person goes to the bahamas.
  • by Anonymous Coward

    What is the point of this post? He states the obvious, then goes on to throw out some bullshit numbers that he admits are bullshit (and are wrong anyway (10^12/10^7 = 100,000)).

    I don't mind the guy looking like a fool, but it wastes everyone's time when idiot moderators mod it up. "Huyuck, garsh, this guy posted numbers, he must be insightful!"

    Bah.

  • And the o.j. simpson trial showed that DNA is not unique either...
  • It's very unlikely that the strength of weight given to fingerprint evidence in courts will lessen very much. Too many past cases have hinged on such evidence and the CJ system doesn't want to open THAT can of worms.

    Think of all of the tens of thousands, if not millions of cases that would have to be looked at again if it were happen. The resources for that simply don't exist.

    Rich...

  • The same with a president. Though he probably should have been executed for treason against these United States.


    He who knows not, and knows he knows not is a wise man
  • IIRC, the reason the DNA evidence in the OJ simpson murder trial was unconvincing to the jury was because the defense proved beyond a reasonable doubt that the labs involved did not adhere to the standards necessary to proved that the correct sample had been analyzed.

    The defense did not attack the concept of DNA analysis but the methods that were used in that particular case of DNA analysis.

    And as bad as it is to possibly let a guilty man go free over a technicality, I would rather see the occasional guilty party go free than allow the police to abuse their powers with impunity. It was the LAPD that screwed up what was pretty close to an open and shut case.

    have a day,

    -l

  • What the article questions is the science behind the method used by FPE's.

    Exactly. That's why a test is needed.

    According to the article, what happens is that FPE's get a (partial, smudged) fingerprint impression and rely on their experience and intuition to determine whether or not the amount of similarities found is sufficient for identification. When the FBI tells them what to look for, suddenly their judgment sways in the other direction.

    No, the article simply gave a couple of anecdotal stories about FPE's being swayed by suggestion. If in general, that's how FPEs work, then it is obvious that they are no more useful than the Psychic Friends Network. However, perhaps those particular FPEs were simply incompetent, and good FPEs make their decisions in a more objective fashion. A test would let us see whether FPEs can really do what they say they can, or simply give the answer the cops want to hear.

    This has very little to do with the extent to which known fingerprint impressions match each other.

    It has everything to do with it if the FPEs are the ones making the decisions.
  • The likelihood that something exists is quantifiable by a non-binary number (i.e. a percentage). The actuality of whether or not something exists is only expressable by a binary number (0 or 1, either it exists or it doesn't).

    The likelihood (or probability) that something exists is directly proportional to the amount of evidence we have that that something exists.

    have a day,

    -l

  • First, the US has about 270M people. That means there are 27,000 other people with similar prints.

    Second, within a city, there might be a higher percentage of people with similar prints than you might expect. Have you ever heard of the birthday problem in statistics? Given a group of 25 people, there's a greater than 50% likelihood that two people share the same birthday. Perhaps a statistician could follow-up with the correct analysis of these figures.

    But it's certainly not 100 other people in the country, and it's probably even higher than you would think.

  • I'm with Jonathan here. What is needed is a survey of the state-of-the-art using real-world like data (grime and partial prints and whatever--someone would need to study and find out what the range of real world fingerprint conditions are), with both hits and misses in the data sets tested. That would give some measure of the effectiveness of fingerprinting as a forensic identification technique.

    On another level, if it really is scientific (and please don't confuse scientific with useful in the real world), there really ought to be some repeatable technique that is used to do this. If there is no such technique, fingerprint identification is not science, even if it is a useful method of identification.

  • I may be missing something here, but it would seem that there must be millions of points where fingerprints could be similar. Yet most police forces are prepared to accept 8, 10, or twelve points of similarity as being conclusive. If so then there, by coralllary, must be millions of points that are dissimilar. It would seem, in fairness, that the courts, or at least defence lwyers, should be looking for dissimilar points not similar ones. If there are six milion possibilities and I only match nine and am convicted it would seem that justice is a joke. So what's new?
  • Next, they'll say that hash collisions can happen. Whoops, I better fix all the code that I wrote, which was based on the assumption that it's impossible.
    ---
  • It's why there is a "reasonable doubt" standard instead of absolute proof; absolute proof is impossible, since you can't disprove the existence of malevolent, shapeshifting teleporting aliens.

    Or even the existence of people if you accept Descartes' _Meditations_ but exclude the ontological argument, but that's a bit much...
  • by SEWilco ( 27983 ) on Saturday November 18, 2000 @11:02AM (#615927) Journal
    Well, it's that process of fingerprint growth that needs to be understood. Without knowing what causes the variations and the probabilities of the various variations, we don't know the odds of two fingerprints being the same.

    That's the point of the article -- we don't really know those odds, as all the popular numbers seem to have been created mostly by guessing.

  • Right the US has the highest prisoner to population ratio in the world, being the best is not enough, why not put everybody in prison: they all have done something sinful anyway and repression is of course the way to a more civil society: and we have the lowest violent crime rate to prove this(not): so using bogus proofs to hype a counter productive justice system is of course the way to go and any questionning of the validity of these techniques is unquestionnably wrong: the world is an evil place and evil people must be destroyed for god did not make them: and this will raise us up to sit beside God himself and we shall all enter nirvana(except the evil ones) where we won't have to reevaluate are childish omnipotent illusions of grandeur, or consider what is wrong with this view of society: we will only have to convince god to stop this stupid experiment and obliterate everyone except us and him and i'm not too sure about him

    Sorry(off topic)Rant

  • by RobertGraham ( 28990 ) on Saturday November 18, 2000 @11:28AM (#615929) Homepage
    Of course not all fingerprints are identical. This fact is not in question. The problem is that not all fingerprint MEASUREMENTS are identical, either. This is a standard "signal-to-noise ratio" problem.

    This is easily verified with standard scientific practices. Grab 10,000 people and give them a metal ball and have them handle it for awhile (without telling them why), then grab clear fingerprint impressions. Give the balls to examiners whose job it is to grab as many fingerprint impressions as they can. Put all this into a database, then start pulling out fingerprints and having examiners match them up.

    What is the error rate whereby fingerprints were matched incorrectly?

    As I see it, the real problem is that people can only think in black or white. The focus of this little question has been if fingerprints are unique or not. The average person isn't mentally equiped to think in terms of "How unique are they?", a vast grey area. Science can never answer black-vs-white questions, but they can certainly measure grey.

  • Just keep in mind that even if only 1 in 10,000 have the same fingerprint, it'd only take a group of 118 people before there would be probability greater than 1/2 that any two fingers in the group match - roughly the size of an average neighborhood.
  • Identical twins and clones do have completely identical DNA, especially the twins. Clones, depending on the cloning method, may have different mitochondrial DNA, but the DNA inside the nucleus of the cell is identical.

    However, identical twins and clones have different fingerprints. This is because the fingerprints are not fully encoded in the genes, and the cell development depends on the growth inside the uterus. They end up with similar fingerprints, but not identical.

    -----

  • Do paper cuts (especially big cuts) change the finger patterns? Just curious... :)

  • Prolly not...cuz there's still the rest of the pattern, there's just a line running through it. Your best bet would be to dip your fingers in acid :P.

  • However, perhaps those particular FPEs were simply incompetent, and good FPEs make their decisions in a more objective fashion.

    Perhaps there are no objective criteria. They cannot even seem to agree on the number of minutae that should match.

    But hey, what do I know. You got me curious, though. Maybe a lack of imagination on my part, but how would a test like the one you're proposing be able to verify the methods used by FPE's?

  • That was the point. It was an attempt at humor.

  • You may or may not be correct about estimating the possibility of a false positive -- but the article centered on a case with PARTIAL prints of TWO fingers. Now, if the disputed evidence had been one partial print, I might have been swayed (were I on the jury) by lack of any corroborating evidence. But, as I'm sure you know, when we are talking about TWO partial prints, one must multiply together the odds of each being a false positive. Let's be very, very generous and say the odds of the false positive for one partial print are 1 in 10^5 (we don't really know, not least because we don't know how much of the full print was in evidence). Then the final odds of a false positive involving two similar partials would be 1 in 10^10. I'm not generally in favor of jailing non-violent persons, but that's good enough evidence of wrong-doing for me!
  • Nah... they'll just keep making new laws until _everyone_ is guilty of _something_. That way they'll have a perfect record of convictions. Everyone in prisons is of _something_. :P
  • Perhaps there are no objective criteria. They cannot even seem to agree on the number of minutae that should match.

    Well, yes, but if FP evidence is to be considered useful, I think there needs to be a demonstration that the different styles of analysis yield the same results in the end.

    But hey, what do I know. You got me curious, though. Maybe a lack of imagination on my part, but how would a test like the one you're proposing be able to verify the methods used by FPE's?

    I was thinking of something along the lines of the tests that skeptics give to people claiming paranormal powers. For example, do different FPEs find that the same impression matches the same person's prints; can the same FPE correctly identify different impressions from the same person as actually being from the same person, etc. A high rate of error would suggest that either there are many incompetent FPEs, or that their methods simply aren't reliable.
  • But when they file them they summarize the data. If I remember correctly they count something like 10 characteristics per fingerprint. Of course, this may have changed. That pore pattern probably would identify you uniquely. But you wouldn't be able to read it from a cleand glass that you had intentionally tried to leave a good print on. So it doesn't have the kind of utility that police need. They need large, obvious features that leave marks with a bit of durability. So that's what they record.

    Caution: Now approaching the (technological) singularity.
  • Like Reagan?

    The tower commission showed he signed the Nov. 18th paper to sell tomahawk missles to the Iranians... The last time I remember a US citizen selling military capabilities to a country who's primary foreign policy was the destruction of the United States was the Rosenbergs...

    and they go the chair.

  • I should really read the original article first but...
    Partial print? That can mean a lot of different things. Did they say how many features were distinct on each print? Did they produce an image to compare against the file? (Images contain a lot more information than the retrieval extract!
    I would probably be swayed by one exact match of an image with a trusted copy of even a third of a finger. Of course, I'd want to do an optical subtraction to see that they actually did match rather than just being close.
    N.B.: This rarely works! Finger size isn't constant. But I'd be more skeptical if they had to scale one of the images to get a perfect match. And marks of various sorts appear on the fingers as aging happens. Etc. So one would need to know when the original prints were taken, etc.
    P.S.: I am NOT an expert in the field. And things may have changed since I browsed it a few decades ago. But the real reason that most fingerprint evidence is bad is the quality of the retrieved print, of which partial is only one of the problems. Consider also: smear, stretch (what was the surface?), scratches (a kind of partial). Of course, if the print was left in warm parafin, then you're in luck. But that, of course, is quite rare.

    P.P.S.: The entire theory of the jail system is faulty. It creates a social order that reinforces criminal behavior. It also encourages sadism by both the jailors and the "top cons". See the partial experiment at Stanford during the '70s. (They had to cancel it because the students acting as jailors started to go out of control!) Jail should not act to reinforce either criminal associations or dominant/submissive behavior. I should act so as to destroy criminal social groupings. The best answer I've come up with is true isolation (meaning, esp., that the jailors can't get at them). I favor welding them into a cell with a bed, and exercise machine, and a computer with a modem. No outgoing phone calls. Good encryption for e-mails from the lawyer (no telephone, but private contact with the lawyer must be possible. So have a restricted list of folk that can contact by e-mail. And the lawyer has the right to directly transfer zip disks (so long keys can easily be used without being subject to interception at key creation time). Food delivered by Bellamy tube. The lawyer must, not may, be present whenever the cell is unsealed. And short sentences. (Short, of course, is relative.)

    Just my thoughts.
    Caution: Now approaching the (technological) singularity.
  • And then there's the matter of definition. I believe that a circus recently (Barnum and Bailey? 1980's?) was exhibiting a goat that had been surgically treated to have one horn in the center of it's forehead. It's supposed to have looked a lot more like a Midieval unicorn than a horse would (beard, shaggy hair around the feet, etc.) But it doesn't look like what someone who has watched "The Last Unicorn" thinks a unicorn should look like. So...
    Was that a unicorn?

    Caution: Now approaching the (technological) singularity.
  • Our legal system is more and more trying to use gorge jetson way of dealing with their problems. They don't like explaining that they think a person is guilty. They want to say we found the prints we feed them in to the computer and our can the name of the defendant. Fingerprints don't lie and so he must be the one. This is wrong on many levels first My prints on a weapon says I may have touched it not that I killed anyone. Example I read where the FBI arrested a woman because a threat letter with "her prints" was sent to the Israeli embassy. All she had to do was load the printer or copier but that does not matter. It was found that she in fact was set up. But the embassy sent the letter to the FBI and the but it in there system and here name came out. When you think of it, it is very easy to frame some one this way. Second Partial fingerprints are just like other partial fingerprints. The pressure on FPE to get a name to spit out is huge. The FBI collects Fingerprints by the 100's of millions and one day you may find that it is your name the computer spits out. The reason FPE believe that they are full proof is because they what and even need to believe they are. As long as the system is believed to be full proof and once the computer spits out a name very little effort is put into finding any one else that may have done it. Push button police work is not good. But as long as the system can get away with it it is what we will get. Dont let any one have your prints if you can help it.
  • Anything that leaves a permanent mark changes the fingerprint pattern. Paper cuts would have no effect on the retrieval algorithim, which depends only on certain factors specified by a human examiner.

    Actually, even sanding your fingerprints of creates no permanent change. (They grow back quickly into the same pattern.) I do understand that there is a technique involving high speed wire brushes that replaces the current pattern with a linear one. But you would need to be truly desperate, and the fact that you intentionally removed the prints would be obvious.

    Caution: Now approaching the (technological) singularity.
  • Not only did they get the chair, they were very likely framed. I don't believe that that was really proven, though. (Can't pay close attention to everything!)


    Caution: Now approaching the (technological) singularity.
  • by Anne Marie ( 239347 ) on Saturday November 18, 2000 @04:25PM (#615946)
    The problem isn't whether fingerprints are unique (although it's an interesting point that their uniqueness has never been proved). For all the author cares, they are unique. It's irrelevent to his chief argument.

    The problem is that exact complete fingerprints aren't used in forensic investigation. Mere fragments are. And not just fragments; sloppy fragments, read by making impressions with the detective's dust and transfered onto paper. The question is therefore whether those fragments are unique relative to other fragments, given the additional fudge factor in how they're read, and whether the use of fragments instead of complete fingerprints is sufficient.

    People need to work on their critical-reading skills.
  • Wouldn't it just be a helluva lot easier to say "Unicorns do not exist", and then you prove that they do (only have to find 1 instance). That's how science works.

    If it worked your way, then we'd all be running around spouting out "Flying pink invisible elephants exist!" and "There's an ultra-magneto-opto-electro-infrared ray coming out of my anus", since no one's ever bothered to try and disprove those statements...well, AFAIK, anyway. And, according to your comment, since no one's "searched for the evidence" of these things and, thus, no one's "fail[ed]", it must be likely that these things do exist. (Since by failing, they are making it less likely that they exist, we must start with a 100% assumption rate, right?)

    You're probably right about Philosophy, however, since Philosophy pretty much deals with the unprovable.
  • Good post, ins, but I want to pick one little nit.

    coup-de-gras

    It's coup-de-grace. "Gras" means fatty or oily in French.

    I'm sick of people misusing coup-de-grace. It means "stroke of mercy" and the term was originally associated with executions. For instance, in a firing squad execution the riflemen shoot the victim and then someone finishes off the victim with a coup-de-grace, that is, a pistol shot to the head. So it's not just a fatal blow, it's a humane act too.

  • If we really want answers, why don't we just turn this over to distributed.net?

  • (Since by failing, they are making it less likely that they exist, we must start with a 100% assumption rate, right?)
    Actually, no. (Slash doesn't support MathML -- and your browser probably doesn't either -- so you'll have to put up with words instead of formulas.)

    Suppose that there are N objects in the universe, and I've observed none of them. What's the probability that at least one of them is a unicorn? Well, given that I know nothing about the relative likelihood of Unicorn-ness among objects, the most likely a priori estimate of the likelihood of a Unicorn is given by quantifying across all possible predicates on the Universe, and computing the probability that IsAUnicorn(x) is true for some x. (After all, the IsAUnicorn predicate is just another predicate. I don't know its characteristic function, but it's got one.) Then it's easy: the Universe is finite, and so there are only finitely many predicates on it, and (drumroll please)...exactly one of those predicates has no elements!

    So, our estimate of the probability that there exists at least one Unicorn, given that we have no evidence speaking to the question, either way, is 1 - 2^(-N), where N is the number of objects in the Universe. Thus, it is very, very likely that there exists a Unicorn, in default of any evidence -- but it is not quite certain.
  • o i thought it were

    out of sight out of mind

    of course under the new Moron administration itll be

    what, me worry?

    yours wdk

  • A cop who falsifies evidence should go to prison.

    Bill Kurtis pointed out the other night that in California, a false witness in a capital trial faces a capital trial of his own. But of course the racist LA prosecutors would never bother to charge a fellow good white racist cop for framing (or at least buffing up the evidence against) an uppity rich nigger, never mind set him up for death.

    Kurtis tried to play it as though it made conspiracy unlikely. But conspiracy was not necessary for the evidence tampering. The only conspiracy on the prosecution of the Simpson was an amalgam of inflated egos.

    I was amazed they were so cocksure as to try him for both murders together... they should've kept one in reserve in case they f*cked up like they did. Then they whiningly blame the jury, who they'd approved. But the jury did its job: there was lots of room for reasonable doubt, especially (to me) in the vaunted "scientific" evidence... to drag this back to the topic at hand.

    As I understood what was presented... I refused to watch the trial voraciously; all I saw were snips in evening news and the presentation of the verdict, and documentaries... the DNA evidence went something like this: "this sample show this little marker, which occurs in fraction X of humans ... and it shows that little marker, which occurs in fraction Y ... thus only XY of humans have the combination, and the possibility of there being another person matching this sample is practically nil! You must convict!"

    My problem is double: a) how do they know X and Y? When was my DNA sampled, or that of anyone else I know? When were the billion-plus Chinese sampled? (Or are they ignorable for the Simpson trial, which merely begs the question of who isn't ignorable, and were they scientifically sampled?)

    And b) how do they know these markers are statistcally independant, that XY is actually their fraction for the population? While I'm willing to grant they may know X and Y well enough, the statistical indepedance (or lack thereof) takes much more analysis to know than than I believe has been done. The prosecution would have to go into serious background to make their "scientific" evidence credulous to me. (And they would have had to handle their case evidence scientifically... a grad student wouldn't get a masters based on labwork of that quality; that anyone's life hung on such bullshit makes a strong argument against capital punishment.)

    No... the Simpson jury had ample room for reasonable doubt as far as I can tell, and whining about it is just sour grapes. The prosecution got full of its own importance and deserved to lose the case if that's the best they could do.

  • I agree that jails are merely almost isolated and very unhealthy social systems that reinforce the very worst behavior in both guards and prisoners. But isolation cannot teach anyone how to alter their behavior; it is used, sparingly, with children because a "time-out" gives them time to reflect rather than react. After childhood is over, the qualities of imagination and openness which make time-outs useful are almost always stunted, particularly in the types of persons who end up (justly or not) in prisons. I certainly would not want prisoners who had been held in complete isolation released into my society again after a "short" term!

    We have learned a lot over the hundreds of years we have been locking up criminals, the insane, "delinquent" and "incorrigible" children, and other troublesome types. Unfortunately, we put almost nothing of what we collectively know into solving the problem of violent behavioral deviance. Why? The same reason we don't bother to raise children properly (at least paying attention!); nurse ill persons properly (that is, caring for them, trying to help them rest and sleep so their bodies can heal themselves); or teach properly: It's a lot of work! Hard work... work that requires love. (Love is an active, transitive verb -- seeking the good of the other; it's not some mushy emotion.)

    Except in the case of violent offenders, the best technical solution for many crimes is probably an unbreakable monitoring bracelet and frequent supervision, with the offender remaining in touch with family, employment, etc. This is why the modern trend is to release prisoners into half-way houses before their sentence is completely over: They need routines, social contacts, a monitored transition into daily life.

  • They don't claim that fingerprints are not uniqe, and they don't claim that it's 'no more accurate that handwriting analysis'.

    They simply claim that, according to principles of science, it is merely an *assumption* that no two fingerprints are the same. It is not a FACT.

    They call into question not whether or not fingerprinting is of use, but whether or not fingerprint evidence should be taken as absolute. They cite the lack of an acknowledgement of an 'error rate', as any scientific method must have.

    The point is, courts will jail people for life on fingerprint evidence, yet no modern (or historical) scientific study has *ever* been done to determine how accurate this is. No proper error rate studies have been done. They never take a thousand people and get them to leave prints all over different things, then lift them, and test to see how things work.

  • and even further off-topic...

    Reminds me of the old guy in The Shawshank Redemption. They let him out after many decades of "rehabilitation". He had been so isolated from society, so totally aloof, that he could not bear living in the foreign real world. So he hung himself.

    Sometimes it just seems easier to jam our problems in a small dark hole and ignore them instead of actually trying hard to fix them.
  • So your conclusion is to continue to lock up innocent people, because the court system won't be able to consider new facts? I guess we have found a Bush voter.

    Did you ignore what I read or simply not read it at all?

    MY CONCLUSION, was that the CJ system won't likely SUDDENLY decide that fingreprints aren't very unique for the reason stated in my previous post.

    That conclusion has NOTHING to do with my personal views or for whom I voted. What I would do is likely DIAMETRICALLY OPPOSED to what the system will do.

    And people wonder why our standardized test scores are as bad as they are... based on posts like this idiot AC's it's no surprise.

    Learn to ACTUALLY read... as opposed to mouthing the words.

    Rich...

  • It was interesting to read in the article that judges have recently had to come up with a better definition of science than "generally accepted" (which would make virgin birth science I guess). One of the requirements they cited was 'falsifiability'. I find this interesting for this reason: falsifiability is crucial for developing science but surely it is redundant in court. Suppose someone wanted to use X in court to prove A is true rather than B. If A is different from B and their argument is sound then this argument itself forms part of a test of the falsifiability of X. If, on the other hand X isn't falsifiable then there is no difference between A and B and so there is no reason why anyone would want to bring X as evidence. So it seems to me that 'falsifiability' is not a useful criterion for deciding whether a 'science' should be used in court (though I'm also saying it's not 'wrong' either). What does anyone else think?
    --

I have hardly ever known a mathematician who was capable of reasoning. -- Plato

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