You are exactly right, one6ylady! The average IQ is 100 points. Then it is a "curve" so that fewer people have 110 points, and even fewer people have 120 points and so on. The same is true going "down" too - that fewer people have 90 points, even fewer have 80 points.
Interestingly, they don't really think you can "do anything" to raise your IQ - but you most definitely can lower your IQ through brain damage - car accidents, drugs, and so on. So I wonder if the average IQ of all children born is 100 - but that by the time a population gets to be aged 60, if the average IQ is now lower because of all the drug users and people who were in accidents!
PM me your address and I'll send that book out to you!