**
**

Chapter
4 Risk: Thrill-seeking genes take us for a ride

**Taking
risks is costly but fun. ** Have you heard about the new state lottery
game? It’s called, "Take a dollar and throw it in the trash."
Actually, that’s not quite fair. State lotteries return about 50%
of the amount wagered, so the game is more aptly called "Take fifty
cents and throw it in the trash."

Why do
we derive pleasure from making terrible bets? Part of the explanation
is that we are terrible mathematicians. We can’t seem to calculate
odds correctly. Take the big drawing in the California state lottery,
for example, where a bet consists of picking six numbers between 1 and
51. To win, these six numbers must match, in any order, the six randomly
drawn numbers. Given these rules, what is the chance of winning? Write
down an approximate answer.

Here’s
another brainteaser. Chinese families place a high value on sons, yet
the Chinese government exerts extreme pressure to limit family size.
Let’s assume that the chance of having a girl is exactly 50%, but
every couple stops having babies once they have a son. So half of the
families have just a single boy, a quarter of the families have one
boy and one girl, an eighth have one boy and two girls, etc. In this
scenario, what percentage of Chinese babies will be male? (The answer
is below.)

One more.
Imagine that you are a doctor and one of your patients asks to take
an HIV test. You assure her that the test is unnecessary as only one
woman out of a thousand with her age and sexual history is infected.
She insists, and sadly the test result indicates viral infection. If
the HIV test is 95% accurate, what is the chance that your patient is
actually sick?

Here are
the answers. Let’s start with the HIV test. When doctors and staff
at Harvard Medical School were asked this question, the most common
answer was a 95% chance that the patient was sick. They missed the mark
by a mile ...

Back
to Excerpts