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This kind of screening is extremely fucked up because average people are terrible statistical reasoners. A 99.999% accurate DNA test will find mostly innocent p
by fipple 8y ago
This kind of screening is extremely fucked up because average people are terrible statistical reasoners. A 99.999% accurate DNA test will find mostly innocent people if applied to a database of tens of millions of people. And even without corroborating evidence, juries will convict on the DNA because average people aren’t wired for this kind of statistical reasoning.
- fixermark 8y agoThe defense will need expert witnesses to explain why genealogical-resolution matching is unreliable, but any defense attorney worth their salt should have a stable of such witnesses; the difference between "A 100% correlated match between DNA at a crime scene and the suspect's DNA" and "An N% correlation between a suspect's DNA and a suspected relative of the suspect" is pretty clear even to this layperson. IANAL, but even without the expert witness, defense should be able to throw enough doubt for a criminal case defense with a line of questioning that begins "If the DNA matched to person Q in the DNA database and not to my client, why is person Q not the one being charged with this crime?" Defense can then move from there to the observation that the match to a relative in the database merely narrows the field of subjects to a whole family tree of relatives of the matched individual. (Note that in this case, the police used the geneology matches as a tool to focus suspect list, not as primary evidence in a murder trial. That's more in the realm of "Looking for everyone in town who buys that brand of cigar" than in the realm of "Your dad's DNA got you sent to prison!!!").