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In your extreme example you can see that people in the B' group (those who don't have black hair) can be safely excluded as suspects. So even in this artificial
by barking 14y ago
In your extreme example you can see that people in the B' group (those who don't have black hair) can be safely excluded as suspects. So even in this artificial example you can see that knowing P(B|A) is of value.
- jlgreco 14y agoYou seem to have missed the part where the extreme example is not real life. If you exclude people without black hair from suspicion, then the baddies will find someone without black hair. You cannot assume P(B|A) will not be modified by the policies you adopt. ...well, you can if you are the TSA and don't actually have to answer to anybody.... P(B|A) will never be 100% anyway though, so even if the terrorists were unable to adapt it would not matter. The point is that even in the absurd event that you found a P(B|A) that was 100%, it doesn't mean it is useful. Or do you actually think that screening for black hair in the example would be worthwhile?
- barking 14y agoYou seem to have missed the part where the extreme example is not real life Actually, I referred to your example as both 'extreme' and 'artificial' in my previous post. Since the example was constructed to make your point as obvious as possible I was just pointing out that in fact P(B|A) was actually useful even in that example. Sorry for the delay in responding, I gave up yesterday because there was no option to reply even after a very long time.