For those of you who recall last week's Introduction to Airline Investing, here is the first in what may become a series of more advanced lessons:

When the overall market moves up or down, some sector's stocks move with it but at a higher rate. This is called leverage, or "beta" for the cognoscenti.

Airlines have a special and unique beta relationship. They follow the "x5-x.5 (90-10) Rule." Here's how the rule works. When the market moves down, airline stocks move down at about 5x that rate. When the overall market moves up. airline stocks move at about a .5x rate; 10% of the time this is up with the market, and 90% of the time it is down in spite of the market. You can check out today's action for a real-world example.

We hope these lessons are helping everyone be better airline investors.