Yeah, that book gave me a few simple tools like that to evaluate a lot of things.
Another example... This test reduces the risk of dying by this type of cancer by 50% and only costs $1,000 ever five years. Clearly it's worth it right?
Well, the risk of dying from that type of cancers is 3 per 100,000. By reducing the risk 50%, you've brought that down to 2 and saved one life per 100,000 at a cost of $100,000,000 every five years.
If you spent that money in another way, could you save, OMG, TWO lives for $100,000,000? I bet you could.
What does this have in common with the DNA case? In both cases, people are lead astray by looking at percentages. They should be looking at absolute numbers.
I know this is OT, but one last example.
People are told that the test for HIV is 100% accurate because it's actually two tests - a gram negative and a gram positive. If it says you have HIV, it means you have it. Doctors tell people this all the time.
That's not what it means. It means that if you have HIV, the test is basically guaranteed to detect it. If it says you're clean, you can stop worrying.
But it actually has a 1 in 1,000 error rate of false positives. The rate of HIV in the monogamous heterosexual male population is 1 in 10,000. So if you're a monogamous heterosexual male and you test positive for HIV, there isn't a 99.999999% chance you have it. There is a 10% chance.
The author of the book tells the story of a man who lost his job, house and wife only to find out three years later that he didn't have HIV. He has stories of people convicted on DNA evidence just because they were a random match only to have someone else, who also matched the DNA, get caught for the crime later.
