[zyxley]

Uh... it's all right there in your link, across several sections that analyze specific parts of the data.

> Black defendants are 45% more likely than white defendants to receive a higher score correcting for the seriousness of their crime, previous arrests, and future criminal behavior.

> Women are 19.4% more likely than men to get a higher score.

> Most surprisingly, people under 25 are 2.5 times as likely to get a higher score as middle aged defendants.

> The violent score overpredicts recidivism for black defendants by 77.3% compared to white defendants.

> Defendands under 25 are 7.4 times as likely to get a higher score as middle aged defendants.

> [U]nder COMPAS black defendants are 91% more likely to get a higher score and not go on to commit more crimes than white defendants after two year.

> COMPAS scores misclassify white reoffenders as low risk at 70.4% more often than black reoffenders.

> Black defendants are twice as likely to be false positives for a Higher violent score than white defendants.

> White defendants are 63% more likely to get a lower score and commit another crime than Black defendants.

Calling out one specific section that doesn't show bias doesn't magically exonerate the rest.

[yummyfajitas]

None of these things are evidence of bias.

The algorithm is biased if it's giving the wrong score due to race or redundantly encoded race. To show that the algorithm is biased, you need to show that (score, race) pairs are more predictive than (score, ) singletons.

Line [36] and [46] both attempt to address this question. The only one of these which is statistically significant is "race_factorOther:score_factorHigh" in line [46].

The other things you bring up are interesting, but do not show bias. At best they show disparate impact which isn't remotely the same thing.

[jdp23]

"Oh sure, this algorithm is much more likely to have false positives on blacks, and much more likely to have false negatives on whites, and the results are that blacks are more likely to treated more harshly by the system. But it's not biased because of the definition of bias I'm using!"

Orwell would have loved "disparate impact isn't bias" :)

[yummyfajitas]

Clearly statistics terminology is confusing you. The definition of bias is E[\hat{\theta} - \theta]. The definition of disparate impact is a predictor computing different means/quantiles for different protected classes.

https://en.wikipedia.org/wiki/Bias_of_an_estimator

https://en.wikipedia.org/wiki/Disparate_impact

To understand this intuitively, here's a simple thought experiment.

Consider Captain Hindsight, a predictor which returns the right answer 100% of the time. By definition, E[\hat{theta} - \theta] = 0, i.e. zero bias. (Also zero variance.)

Now suppose that blacks have a higher recidivism rate (hardly implausible, ProPublica's analysis suggests they do with p < 0.01).

Captain Hindsight - being 100% accurate and having no bias - must predict that blacks have a higher recidivism rate. Yet because Captain Hindsight predicts a higher recidivism rate for blacks, he now has disparate impact.

Seriously, you are calling standard mathematical terminology Orwellian? What's your angle here?

[zyxley]

Your thought experiment here is incorrect, given that the analysis compares COMPAS results to actual recidivism rates and shows over- and under-prediction in comparison to them.

[yummyfajitas]

The thought experiment is a mathematical proof that the two concepts are causally unrelated, nothing more. I really suggest you brush up on your basic math - you seem to not be following along.

Your claims about the emirical means of recidivism rates do not prove what you think they prove. Different races might be misclassified at different rates for a variety of reasons - e.g., one race might be affected more by some high-variance predictor, or there could be composition effects (e.g. the pdf of blacks|high score might be different than whites|high score).

The way to factor out whether they scores are biased is to do the cox survival analysis with interaction terms. Which they did. You just don't like the result.

Could you clearly lay out the statistical argument that you believe implies that E[\hat{\theta} - \theta] > 0?

[zyxley]

> Could you clearly lay out the statistical argument that you believe implies that E[\hat{\theta} - \theta] > 0?

Again: I don't care about your domain-specific definition of "bias". I care about whether the end result of this secret algorithm is unequal and inaccurate treatment of different demographic groups.

[jdp23]

Clearly the idea that words have meanings beyond statistics terminology is confusing you.

And no, I'm not calling standard mathematical terminology Orwellian. What I'm calling Orwellian is your describing a biased system as unbiased (by attempting to reframe the discussion around a specific statistical definition, chosen by you).

[TheCoelacanth]

It is consistently giving incorrectly low scores to white subjects and consistently giving incorrectly high scores to black subjects. That is clearly bias, at least in the colloquial sense.

[selectron]

The real question though is whether this is because the model is biased, or whether it is because the two populations have different levels of risk. If group A had a higher risk than group B, than I would expect the model to have a higher rate of false negatives for group A than for group B. This is just because the model is more likely to (correctly) assign members of group A as high risk, and some of these classifications will be wrong. To check for bias you have to control for this base rate difference.

[yummyfajitas]

The degree to which it does this cannot be distinguished from random chance (p > 0.05).

If the predictor were biased then you could build a more accurate score based on both the original scores and race_factorBlack:score_factorHigh (and other interaction terms). I.e. you'd be building a new bias in to cancel the old bias, leaving an accurate predictor.

Their analysis doesn't show that this is possible.

[TheCoelacanth]

p > 0.05 is the type of cutoff you would see to get published in a peer-reviewed paper. Such a high bar of evidence is not necessary in this situation. To prevail in a civil suit, a person harmed by this algorithm would only have to prove that is more likely than not that the algorithm is biased.

[zyxley]

> but do not show bias. At best they show disparate impact

I have no interest in playing but-what-does-the-exact-dictionary-definition-say semantics games.

[escape_goat]

> I have no interest in playing but-what-does-the-exact-dictionary-definition-say semantics games.

That's certainly reasonable, but actually you're responding to a statistical argument about a statistical study, made by a statistician.

It would seem tendentious to argue that these numbers are unconnected to systemic social bias, but he is not making such an argument.

[jdp23]

The funny thing is that the dictionary definition supports your point, not yummyfajitas.

bias: prejudice in favor of or against one thing, person, or group compared with another, usually in a way considered to be unfair.

[belorn]

If you are going to argue a single dictionary definition, you should immediately stop holding a mouse when using a computer. Rodents don't like being held for long times, be connected electrically to a machine, nor do they like being rubbed on a pad.

[zyxley]

I think the obvious answer here is to genetically engineer a "computer mouse" that can mentally work complex algorithms, as supplied via a pet training clicker.

Then, you'll be able to click your computer mouse to solve problems.