Prob theory

also called evidence theorem = how much you should trust the evidence that comes in.

short example

car alarm is frequently regarded as a false alarm, and we usually ignore it.

long example

	Cancer (1%)	Healthy (99%)
Test pos	80%	10%
Test neg	20%	90%

1% of people have cancer

Q: what’s the chance we really have cancer if we get a positive result.

A: ~ 8%

False positives skew results.