> If you have a single piece of exclusionary information, it's ludicrous to conduct a bunch of searches which are guaranteed to be worthless in the name of equality. (Leaving aside the accuracy of the tip for now.) And yet on a broader level, it's apparent that profiling can have all kinds of awful side effects.
The problem is that the main true benefit of the information is to exclude people, but that isn't how people use it.
Suppose there are 2 million people in an area and you know some demographic information about the perpetrator that will allow 95% of them to be excluded. That is useful information.
But the probability that a random person in the relevant demographic is the perpetrator is now 0.001%. The demographic contains 100,000 people and one perpetrator.
The fallacy is in assuming that just because not being in the relevant demographic is enough to exclude you, that being in the relevant demographic should by itself be enough to suspect you.
No, it's not. BRF has two components: Generic information about the frequency of events and specific information about the case in question. The item in question doesn't contain these. The item in question is a much simpler point.
> But the probability that a random person in the relevant demographic is the perpetrator is now 0.001%. The demographic contains 100,000 people and one perpetrator.
That's still a much higher probability than 1/(2 000 000) so I am not sure what is your point there to use numbers.
the point is that it's not a useful indicator for stopping random people.
"Oh, to catch the thief we are going to stop 100000 people" sounds absurd, after all.
Of course you can use the clue to exclude a bunch of people, but were you going to go around arresting random people on the street without this? Of course not, so why do it after.
The problem is that the main true benefit of the information is to exclude people, but that isn't how people use it.
Suppose there are 2 million people in an area and you know some demographic information about the perpetrator that will allow 95% of them to be excluded. That is useful information.
But the probability that a random person in the relevant demographic is the perpetrator is now 0.001%. The demographic contains 100,000 people and one perpetrator.
The fallacy is in assuming that just because not being in the relevant demographic is enough to exclude you, that being in the relevant demographic should by itself be enough to suspect you.