More Sex Is Safer Sex . . .

Assessing Evidence:

You are given an HIV test despite the fact that 99% of the people in your demographic group are uninfected. You think the test is a waste of your hard earned $. You, do, get a hellacious shock when your test results come back: INFECTED!!! Time for self-defensetration? Perhaps. However, the HIV test is wrong 5% of the time and this means that there is roughly a 5% chance that you're okay? WRONG!!! More like an 84% chance you're okay.

"Why 84%? In a population of 100,000 people, we've assumed that just 1%----that is, 1,000----are infected. Of the the 1,000 who are infected, 95% [950 people] get accurate (and grim) test results. Of the 99,000 who are healthy, 5%, or 4,950 get inaccurate results that say they're infected. That makes 950 + 4,950 = 5,900 people who got bad [grim] news, and of 5,900, only 950, or 16%, are actually infected. The other 84% are just fine." Footnote on page 91, "More Sex is Safer Sex The Unconventional Wisdom of Economics," by Steven E. Landsburg.

"But if Oswald is right, then much or the world's unemployment is caused by home ownership-----which puts an interesting gloss on the fact that home ownership is subsidized by governments almost everywhere in the Western world." ID at 143.

"Over two centuries ago, a lawyer named William Blackstone declared that it's better for ten guilty persons to escape than for one innocent to suffer. Why ten, as opposed to, say twelve or eight? Because Blackstone said so, that's why. By pulling the number ten out of thin air, Blackstone defiantly refused to think about the trade-offs that go into designing a criminal justice system. But for two centuries, legal scholars have cited Blackstone's refusal to think and mistaken it for an example of a thought. Of course it's a bad thing to convict the innocent. We all know, that, just as we know it's a bad thing to acquit the quilty." ID at page 222.

Unfortunately, imo, we all don't don't that it is bad to convict the innocent. More importantly "we know it's a bad thing to acquit the quilty"??? Shit, I don't belief for a second that even the author, Mr. Steven E. Landsburg, actually believes it's necessarily a bad thing to acquit the guilty. My guess is, and I could be very wrong, more often than not it is better for the guilty NOT to be convicted.

Anyway, the reason I supplied the snippits, supra, is so that readers could get a little more of a glimpse of what his book is about. Also, I liked it much better than Freaknomics. :) The starter, imo, is "Free to Choose: A Personal Statement," by Milton Friedman and Rose Friedman. amazon.com

Correction: Unfortunately, imo, we all don't agree that it is bad to convict the innocent.

I suppose he meant it as a purely hypothetical and dramatic example, but, for the record, modern HIV tests have way higher specifities than 95%. Very close to 100%, in fact.

Otherwise it's a pretty good example of Bayes' theorem, which doctors seem to (either intuitively or due to formal training) have a good understanding of. It's also one of the reasons why they will ask you about your sexual history before they run the tests as opposed to just running them.

I buy the bit about home ownership. I'm personally all for unemployment. Best thing that ever happened to me was losing my job. There's always some way to get a bite to eat ... the hard part is getting respect when you aren't employed. School's always a good trick for fixing that ... :) ...