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  1. #1 forensic scientist 
    WYSIWYG Moderator marnixR's Avatar
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    i once went to a lecture by a forensic scientist where he had a good go at the way his profession is portrayed in television series

    he then gave a detailed description of a real-life case, and showed how using the phrase "is consistent with" is incompatible with the real job of a forensic scientist, who should always use the phrase "is indicative of"

    the first means that amongst a variety of possible causes you decided to highlight one out of many, whilst the second narrows down the number of possible causes to a smaller number

    in the real-life event, the case went to court where it collapsed for lack of evidence - all because the forensic scientist decided it would be nice to take on the role of the TV detective


    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  3. #2 Re: forensic scientist 
    Forum Ph.D. william's Avatar
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    Quote Originally Posted by marnixR
    he then gave a detailed description of a real-life case, and showed how using the phrase "is consistent with" is incompatible with the real job of a forensic scientist, who should always use the phrase "is indicative of"
    Interesting...

    I guess language might be more important here than in other sciences because, in the end, one must convince a jury....

    Cheers


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    Administrator KALSTER's Avatar
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    one must convince a jury
    I really am not a fan of this. Instead of having to prove someone's guilt, you have to convince a jury. People are prone to prejudice, even if they don't believe it themselves.

    Ok, so how conclusive does evidence have to be to convict someone? I mean, is a large amount of circumstancial evidence enough for a conviction? Then also, do forensic investigators calculate the odds of something happening during there investigation? Are they always impartial in terms of collecting ALL possible information from a crime scene? Are their guidelines open to interpretation or are they specificaly written to preclude subjectivity from a report?
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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  5. #4  
    Forum Ph.D. william's Avatar
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    Quote Originally Posted by KALSTER
    one must convince a jury
    I really am not a fan of this. Instead of having to prove someone's guilt, you have to convince a jury. People are prone to prejudice, even if they don't believe it themselves.

    Ok, so how conclusive does evidence have to be to convict someone? I mean, is a large amount of circumstancial evidence enough for a conviction? Then also, do forensic investigators calculate the odds of something happening during there investigation? Are they always impartial in terms of collecting ALL possible information from a crime scene? Are their guidelines open to interpretation or are they specificaly written to preclude subjectivity from a report?

    These are great questions!

    We all are familiar with fingerprints. And we might not think twice about convicting someone who's fingerprints matched ones at the crime scene (assuming we could build a good case upon other evidence, perhaps circumstantial). But are any of us really sure about fingerprints being unique? When fingerprints were first introduced, they probably had to convince the jury of their uniqueness.

    In today's world, the same might be true for DNA. I would have to be convinced of the uniqueness since I never really studied it myself.


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    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
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    Administrator KALSTER's Avatar
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    Well, if you look different to a person, you have different DNA. Not too sure about identical twins though....

    Fingerprints are also unique, but I am not too sure if they can be matched to exactly 100% accuracy. That is why I am asking about the odds. Mitochondrial DNA (if only the upper part of a hair is found)for example can only give an indication of your lineage, I think, so it could at most add to the circumstantial evidence. Then if a certain amount of circumstantial evidence has been collected, do they then work out the likelihood of all of them happening to an innocent person? Or do they leave it up to the jury? Do they leave it up to the District attorney’s discretion if a case can go to trial, or do certain exact criteria have to be met?
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
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  7. #6  
    WYSIWYG Moderator marnixR's Avatar
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    the main thing about this lecture was that the forensic scientist overinterpreted the results and could have misled the jury into convicting an innocent person - the fact that it didn't happen was merely fortuitous

    the lecturer's final words were :

    "if as a result of this lecture i have put some people off from becoming a forensic scientist, then i have achieved my aim - rather that than see people enter the profession in the mistaken belief that they will be the real-life equivalent of a glamorous TV star"

    in short, a forensic scientist doesn't attempt to solve a case : he/she only attempts to unearth evidence so that others can evaluate it
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Administrator KALSTER's Avatar
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    Imagine how it must feel to the guy that gets sent to jail for the rest of his life, knowing he didn't do it Sounds like a good lecture. As I said before, it is disconcerting to know that a bunch of everyday people get to decide your fate, based on the competency of the accusers and prosecutors. That is why I wonder about the efficacy of guidelines , presumably put in place to restrict this kind of thing to a minimum.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
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  9. #8  
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    Quote Originally Posted by KALSTER
    Ok, so how conclusive does evidence have to be to convict someone? I mean, is a large amount of circumstancial evidence enough for a conviction? Then also, do forensic investigators calculate the odds of something happening during there investigation? Are they always impartial in terms of collecting ALL possible information from a crime scene? Are their guidelines open to interpretation or are they specificaly written to preclude subjectivity from a report?
    Right, point by point: Evidence is never conclusive, it is just a piece of the puzzle, like having the page of a book shredded, each line is a piece of the page. The aim is to get as many pieces of it together in a reasonable order that would implicate suspect X without the investigator actually aiming to do so.

    I've not heard of any mathmaticians calculating odds in terms of forensics (except in that show, Numbers) But yeah, we're taught to survey the scene before anything else in case of other dangers such as a secondary explosive near the scene of a bombing.

    No, they're rarely impartial to the collection of evidence, but they do collect as much as they can. The problem is that the procedures to analyse everything would bankrupt any company within a month or two. Forensic scientists process the MOST LIKELY pieces of evidence to have been involved with the crime

    And the guidelines are pretty much set in stone. Each test is done in a specific way so that if needs be it can be replicated and in the remote event that new tests are forged, they need to be tested in numerous facilities. If you have an up to date periodic table, you'll notice the new elements at the bottom of the P block, some very faint. This indicates that one scientist has created the element, but that others have as yet been unable to replicate the experiment.

    Quote Originally Posted by William
    In today's world, the same might be true for DNA. I would have to be convinced of the uniqueness since I never really studied it myself.
    DNA is unique for the most part. As always, there are exceptions. Identical twins do have the same DNA but in general, it is so statistically slight that someone will have the same DNA as you. Last I checked was last year where they came up with about 1 in a billion. (6.4 little versions of me on the planet? - lol) which is even just the small amount of DNA that they test for in the forensics labs. - For clarification, see the edit below -

    It should be pointed out that they do not test ALL the DNA as that would take far too long and be too costly. (But one company has. Look for the 'Human Genome Project', I think there's a book out)

    As for fingerprints, the ridge patterns are created by the bones growing and pushing tissue outwards while you are still in the womb and yes, because they are generally tested in full sets of ten (I'll not explain the system here) the series is unique. As to whether there are two different people with an exact fingerprint match (just one finger) I don't know, but would be highly doubtful.

    The reason I would do this is that the fingerprints are created by random flesh and the patterns are caused by the specific way that the bones grow on a cellular level, but because DNA is a set of codes that are passed on through the parents, there can only be so many possible combinations of DNA (Thus the statistics rather than impossibility.)

    Now for some fun facts - you know when your fingers and toes prune up? this is actually to increase grip under wet conditions, like letting the air out of your tires in winter.

    Certain breeds of monkeys have been found to have evolved ridge detail (fingerprints) on the knuckles of the hand and along the end of the tail.

    And finally, a number of cases were reported some years ago of people missing their fingerprints. It was first thought that there was a criminal element going around and removing them to leave less evidence at crime scenes, but the real reason was much weirder. All people reported without fingerprints actually worked in pineapple farms and after a bit of scientific testing, it was shown that there is an enzyme in pineapples that eats away at ridge detail.

    Ok, that's all from me on this for now...

    -----EDIT-----

    I feel that I should clear this up. This is mine from the other post on DNA:

    DNA is unique, but the tests only measure the most likely variant area. There is in fact a one in a billion chance of a match with someone else using the area that is profiled, but take solace that these matches can be ruled out by profiling other areas of the DNA strands. As there have been snowflakes that are identical, down to a molecular level (how cool is that?) you can take solace in the fact that there will never be anyone quite like you, unless you're an identical twin.
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  10. #9  
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    Quote Originally Posted by KALSTER
    one must convince a jury
    I really am not a fan of this. Instead of having to prove someone's guilt, you have to convince a jury. People are prone to prejudice, even if they don't believe it themselves.
    This is why statistically people are actually less likely to be convicted if they request a bench trial (where there's no jury and the judge himself decides if the prosecution has proved the case beyond a reasonable doubt). It's a lot harder to dazzle a professional judge with circumstantial evidence or bullshit emotional ploys.

    Of course there might be some bias to that statistic, since presumably people who are actually innocent will be more likely to request a bench trial. In cases where the person is guilty and the prosecution actually has good evidence, you probably want to go with a stupid jury that you might be able to trick or confuse.
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  11. #10  
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    Quote Originally Posted by MHFenix
    I feel that I should clear this up. This is mine from the other post on DNA:

    DNA is unique, but the tests only measure the most likely variant area. There is in fact a one in a billion chance of a match with someone else using the area that is profiled, but take solace that these matches can be ruled out by profiling other areas of the DNA strands. As there have been snowflakes that are identical, down to a molecular level (how cool is that?) you can take solace in the fact that there will never be anyone quite like you, unless you're an identical twin.
    Remember, when forensic scientists talk about there being a one in a billion chance of someone matching, they're talking about the odds that a given profile will match another randomly selected profile. But in fact you will still have large numbers of people with identical profiles in your database if you build a DNA database of any significant size. Google "birthday problem" for a detailed explanation of the math. But if the odds of two people matching are one in a billion, then there will be a 50% chance of two people in your database sharing the same profile once your database grows to just 37,233 people. And if you happen to be in the database, there is a 1 in 27 thousand chance that someone else in the database will match you. Still not good odds, but a lot better than the 1-in-a-billion that you might think it would be. And that's for a relatively small 37k person database.
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    Quote Originally Posted by Scifor Refugee
    Remember, when forensic scientists talk about there being a one in a billion chance of someone matching, they're talking about the odds that a given profile will match another randomly selected profile. But in fact you will still have large numbers of people with identical profiles in your database if you build a DNA database of any significant size. Google "birthday problem" for a detailed explanation of the math. But if the odds of two people matching are one in a billion, then there will be a 50% chance of two people in your database sharing the same profile once your database grows to just 37,233 people. And if you happen to be in the database, there is a 1 in 27 thousand chance that someone else in the database will match you. Still not good odds, but a lot better than the 1-in-a-billion that you might think it would be. And that's for a relatively small 37k person database.
    OH MY GOD! Thank you! I explained this to the tutor who taught us DNA and she refused to acknoledge... accno... accept that there was even a possibility!
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