[soVeryTired]

> Is it "bias" if it's true?

I think it's quite common that the quantity you're interested in isn't observable, so you need to proxy it with something. The GP's example is "Person X is likely to commit a crime". If that could be estimated reliably, it would be extremely useful for allocating governmental resources like policing and education.

The problem is "Person X is likely to commit a crime" isn't observable, so a careless researcher might proxy it with "Person X is likely to be convicted of a crime". The latter is actually very different for the former, since it includes factors like a defendent's ability to hire a good lawyer, existing police presence around Person X's neighbourhood, and government priorities on which crimes to prosecute (think crack vs. cocaine in the 80's).

Any good social scientist or economist will be aware of all of this. But once you bake it into a model that doesn't explain itself, you have a mess on your hands. Especially if the model gets more credence than it deserves by people who don't understand it.