How would you know its 90% certainty? Even attempting to measuring certainty has an uncertainty factor in it. We know with some uncertainty the murder rate eac

How would you know its 90% certainty? Even attempting to measuring certainty has an uncertainty factor in it. We know with some uncertainty the murder rate each year, and from this we have some measurable number that a person might be murdered. But we also know that murders tend to occur in non-random ways. At what murder rate should we start to arrest people at random? They are fun thoughts experiments, but as guides for real life they work about as good as extreme simulations which removes mass, gravity and air friction.