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What are the false positive and false negative rates of DNA testing? Paternity tests for example seem to have ~1.1% false positive rates, and that’s comparing a

by gcr 3y ago

What are the false positive and false negative rates of DNA testing? Paternity tests for example seem to have ~1.1% false positive rates, and that’s comparing a single sample to a single other sample. Keep in mind that comparing a DNA sample to a gallery for the purpose of large-scale matching raises the false positive likelihood significantly. I’m not at all convinced that this could be done without convicting innocent people.

paul_funyun 3y ago
A paternity test is harder to get right. If there's a difference in a DNA matching test, that eliminates the possibility. With a paternity test, you're just looking for similarity so there less ways to rule one out
- lazide 3y ago
  Kinda. It depends on how the facility handles the sample, the type of magnification being done, how many points are compared, etc. Some (older) types of tests might only compare a couple hundred locations, or not be particularly picky about how close a match actually is to be a match, etc. And contaminated samples are a big problem
deleted 3y ago
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ajross 3y ago
> Paternity tests for example seem to have ~1.1% false positive rates Realistically I think the existing criminal justice system would be hard put to claim a wrongful conviction rate lower than that, so... I'm not sure this argument cuts the way you want it to. If you have a 99% accurate test of guilt, that seems like more than enough probable cause to continue investigating, and probably good enough to convict with just a little extra corroboration. While there's a privacy argument to be made, I really don't think you're going to get very far arguing that this is going to cause quality problems. Frankly I think it's likely to help with reducing false imprisonment (i.e. by fingering the right suspect earlier, before the wrong one ends up in court).
- Cpoll 3y ago
  There's an old Bayesian thought exercise: Imagine that the test for Condition X has a 1/100 false positive rate (specificity), but X occurs in only 1/1000 people. If you select a random person and they test positive for X, it's more likely that they hit the 1% false positive than that they actually have X. (This comes up all the time in practice). So if you have a database of 10,000 people and 1.1% false positive rate, you're likely to get several false positives. Unless you stop searching as soon as you find a positive, of course...
- breather 3y ago
  > If you have a 99% accurate test of guilt, that seems like more than enough probable cause to continue investigating, and probably good enough to convict with just a little extra corroboration. If you're facing a jury (as you probably are in a criminal case) people have been convicted on far less than this with no other corroboration. It's all in the narrative put before the jury and their understanding of the evidential burden.

by gcr 3y ago

paul_funyun 3y ago

A paternity test is harder to get right. If there's a difference in a DNA matching test, that eliminates the possibility. With a paternity test, you're just looking for similarity so there less ways to rule one out

lazide 3y ago
Kinda. It depends on how the facility handles the sample, the type of magnification being done, how many points are compared, etc. Some (older) types of tests might only compare a couple hundred locations, or not be particularly picky about how close a match actually is to be a match, etc. And contaminated samples are a big problem

deleted 3y ago

[deleted]

ajross 3y ago

> Paternity tests for example seem to have ~1.1% false positive rates Realistically I think the existing criminal justice system would be hard put to claim a wrongful conviction rate lower than that, so... I'm not sure this argument cuts the way you want it to. If you have a 99% accurate test of guilt, that seems like more than enough probable cause to continue investigating, and probably good enough to convict with just a little extra corroboration. While there's a privacy argument to be made, I really don't think you're going to get very far arguing that this is going to cause quality problems. Frankly I think it's likely to help with reducing false imprisonment (i.e. by fingering the right suspect earlier, before the wrong one ends up in court).

Cpoll 3y ago
There's an old Bayesian thought exercise: Imagine that the test for Condition X has a 1/100 false positive rate (specificity), but X occurs in only 1/1000 people. If you select a random person and they test positive for X, it's more likely that they hit the 1% false positive than that they actually have X. (This comes up all the time in practice). So if you have a database of 10,000 people and 1.1% false positive rate, you're likely to get several false positives. Unless you stop searching as soon as you find a positive, of course...
breather 3y ago
> If you have a 99% accurate test of guilt, that seems like more than enough probable cause to continue investigating, and probably good enough to convict with just a little extra corroboration. If you're facing a jury (as you probably are in a criminal case) people have been convicted on far less than this with no other corroboration. It's all in the narrative put before the jury and their understanding of the evidential burden.