henry schaffer asks, "I wonder if the same kind of shenanigans go on with respect to "ballistic fingerprinting" and other firearms-related evidence?"
With regard to other firearms-related evidence the FBI recently (in the last few years) abandoned lead comparisons which they've used for years. These comparisons, from a bullet recovered at a crime scene to bullets found in a suspects possession, was to compare the metal make-up in the lead bullets. Supposedly, bullets from the same production run (box) were very similar and from different production runs (boxes) would not be similar. So, an FBI expert would testify as to the likelihood of the suspect being the criminal perp based on this similarity. Over years, evidence accumulated that such comparisons were too unreliable. It doesn't appear to me that there is sufficient scientific backing for ballistic comparisons to assert a bullet or cartridge came from a particular gun with sufficient reliability for use in evidence (the best I think you can say is they may have come from a particular model of gun). I'd like to see the double blind studies that would prove otherwise. Phil -- > > Joseph E. Olson writes: > > >From the 'net. > > >>> Tangentially Related: State crime lab analyst Kathryn Troyer was > > running tests on Arizona's DNA database when she stumbled across two > > felons with remarkably similar genetic profiles. The men matched at > > nine of the 13 locations on chromosomes, or loci, commonly used to > > distinguish people. The FBI estimated the odds of unrelated people > > sharing those genetic markers to be as remote as 1 in 113 billion. But > > the mug shots of the two felons suggested that they were not related: > > One was black, the other white. In the years after her 2001 discovery, > > Troyer found dozens of similar matches - each seeming to defy > > impossible oddsâ > > > > http://www.latimes.com/news/local/la-me-dna20-2008jul20,0,1506170,full.story > > <<< > > The article is interesting, and must be read carefully to see that > there are two different types* of investigations, and two different > types of "odds" being discussed. This is and has been very well known > and discussed in the Bioinformatics community. > > What is really new is the possibility that the FBI is trying to hide > this information. > > I wonder if the same kind of shenanigans go on with respect to > "ballistic fingerprinting" and other firearms-related evidence? > > --henry schaffer > > *Typically, the police have a DNA sample and check the database for a > match - and want the odds against having a spurious match. > > But the "Arizona search" being discussed is to compare *all* the pairs > of records in the database and see how many spurious matches are found. > The chance of finding a spurious match in this comparison is *much* > higher than of finding a spurious match in the first situation. > > If you want to see a well known example - look for Birthday Paradox > (or Birthday Problem.) (Briefly - you're in a room with 22 other > people. What is the chance that one of them has a birthday which > matches yours? Ans: approx. 22/365 = 6%. What is the chance that any > two people in the room have matching birthdays? Ans: 50%) > > -- The Art of war is simple enough. Find out where your enemy is. Get at him as soon as you can. Strike at him as hard as you can and as often as you can, and keep moving on. -- Ulysses S. Grant _______________________________________________ To post, send message to [email protected] To subscribe, unsubscribe, change options, or get password, see http://lists.ucla.edu/cgi-bin/mailman/listinfo/firearmsregprof Please note that messages sent to this large list cannot be viewed as private. Anyone can subscribe to the list and read messages that are posted; people can read the Web archives; and list members can (rightly or wrongly) forward the messages to others.
