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> Are vein patterns even static? What does that matter? Imagine some other characteristic that definitely changes over time lets say your clothing. The case in

> Are vein patterns even static? What does that matter? Imagine some other characteristic that definitely changes over time lets say your clothing. The case in question had an expert saying: “Yes, the person recorded in the video is wearing the exact same clothes that we know the father was wearing the night of the incident, and that he is also wearing to court today. Now mind you, we dont know the exact statistical lilelihood that someone else would wear the exact same pants, shirt, tie, shoes and hat.” Your attempted counter argument is “yes ok, that is definitely the same clothes that the perpetrator was wearing and that the defendant wore that night and today, but he could change his clothes tomorrow, so…”

treesprite82 5y ago
Assume we're starting with a 1% prior of some person being the the perpetrator of a crime. Consider some completely static characteristic. If the suspect is the perpetrator then there's an 100% chance they still have this characteristic, whereas if the suspect is innocent then there's a 10% chance they have this characteristic just by coincidence. Therefore if the suspect turns out to have this characteristic, you should update your prior to (1*0.01)/0.1 = 10%. Compare to some dynamic characteristic. If the suspect is the perpetrator then there's an 20% chance they still have this characteristic, whereas if the suspect is innocent then there's a 10% chance they have this characteristic just by coincidence. Therefore if the suspect turns out to have this characteristic, you should update your prior to (0.2*0.01)/0.1 = 2%. At the extreme, a completely dynamic characteristic. If the suspect is the perpetrator then there's a 10% chance they still have this characteristic, whereas if the suspect is innocent then there's a 10% chance they have this characteristic just by coincidence. Clearly in this case you shouldn't update your prior at all.

treesprite82 5y ago

Assume we're starting with a 1% prior of some person being the the perpetrator of a crime. Consider some completely static characteristic. If the suspect is the perpetrator then there's an 100% chance they still have this characteristic, whereas if the suspect is innocent then there's a 10% chance they have this characteristic just by coincidence. Therefore if the suspect turns out to have this characteristic, you should update your prior to (1*0.01)/0.1 = 10%. Compare to some dynamic characteristic. If the suspect is the perpetrator then there's an 20% chance they still have this characteristic, whereas if the suspect is innocent then there's a 10% chance they have this characteristic just by coincidence. Therefore if the suspect turns out to have this characteristic, you should update your prior to (0.2*0.01)/0.1 = 2%. At the extreme, a completely dynamic characteristic. If the suspect is the perpetrator then there's a 10% chance they still have this characteristic, whereas if the suspect is innocent then there's a 10% chance they have this characteristic just by coincidence. Clearly in this case you shouldn't update your prior at all.