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NRC I's approach: test additional loci. (Dr. Larry Mueller, UC Irvine)The distinction between finding a match between an evidence sample and a suspect sample and finding a match between an evidence sample and one of many entries in a DNA profile databank is important. The chance of finding a match in the second case is considerably higher, because one does not start with a single hypothesis to test (i.e., that the evidence was left by a particular suspect), but instead fishes through the databank, trying out many hypotheses.If a pattern has a frequency of 1 in 10,000, there would still be a considerable probability (about 10%) of seeing it by chance in a databank of 1,000 people. Although there are statistical methods for correcting for such multiple testing, the committee considers that approach unwise, because it requires that the population frequency estimates of genotypes are accurate to a degree that is unlikely to be achieved (because sample sizes are limited). There is a far better solution: When a match is obtained between an evidence sample and a databank entry, the match should be confirmed by testing with additional loci. The initial match should be used as probable cause to obtain a blood sample from the suspect, but only the statistical frequency associated with the additional loci should be presented at trial (to prevent the selection bias that is inherent in searching a databank). Forensic DNA typing laboratories should recognize that they will require additional loci beyond those used in the databank to prove a case against a suspect. Preparations should be begun now to have additional loci characterized and available for general use before any DNA profile databank comes into common use. MaterialsPresentationNational Resource Council (NRC). DNA technology in forensic science. Washington DC, National Academy Press; 1992. |
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