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    In a nutshell, my understanding is that team A has an overall higher base line rate compared to team B, so that the number of errors on team A is higher than team B, given the same percentage error. This is causing a ruckus because people want to compare absolute numbers. And if you want to equalize the absolute numbers you need to allow for a higher error rate on team B than A.

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      Northpointe, the company that sells COMPAS, said in response that the test was racially neutral. To support that assertion, company officials pointed to another of our findings, which was that the rate of accuracy for COMPAS scores — about 60 percent — was the same for black and white defendants

      What does accuracy mean here?

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        Reading between the lines a little bit (so I could be wrong): threshold the scores at some level, dividing them into “low risk” and “high risk” scores. An accurate prediction is a case where either a defendent given a high-risk score is re-arrested in the following two years, or one given a low-risk score isn’t re-arrested in that time. Accuracy is accurate predictions divided by total cases.

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          Of course the unstated assumption is that the false positive (Arrested but actually innocent, but found guilty after trial) rate for actual arrests is 0%.

          For low income defendants, we know this to be unlikely because they are appointed a public defense attorney, who is likely to ask them to plead guilty for reduced charges. Public Defense Attorneys do this because they do not have time to adequately defend each case, so if they try to fight the charges they’ll likely lose even if they are innocent. This isn’t a case of the Defense Attorney trying to get out of work, this is frequently literally the most advantageous path their client can take. This unfortunately clouds a lot of crime metrics, and until our court system improves we won’t get good enough data to make conclusions going forward.

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            Interesting. My partner is a lawyer and told me that murder trials can cost $100k (this is in Canada) so only the wealthiest people could afford a private defense attorney. But regardless most of their murder cases are funded by the government (meaning they make around ~10k/yr in income). Otherwise they will be mortgaging the house and borrowing from family.

            The bigger problem that often comes up is most people talk to the police way to much. So the only defense they are often left with is challenging civil rights abuses for the search warrants or what not. As the police typically have enough evidence. I’ve watched a number of police interviews from their cases and every time they end up saying something they shouldn’t.

            The third thing that really doesn’t get enough attention in the media is how cell phones have made the polices job 10x easier. That data which gets pulled in every case and most of the time it’s useful. Not a good era to be a defense attorney!

            These three combined contribute to the 90%(?) plea deal situation.

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              nor is it a good time to look guilty but be innocent :(