You can add another item to the list of things the market has to be worried about.

In this month's Portfolio magazine, Michael Lewis wonders if the Black-Scholes formula -- the formula used to calculate and manage risk throughout the financial world, including determining the risk of trade positions and hedging strategies -- is flawed.

The Black-Scholes formula is an advanced mathematical formula generally credited with revolutionizing options pricing. Its assumptions are the basis for short trades and options designed to protect a trader against losses, no matter how much the market falls.

However, as Lewis outlines, while the formula has been good, it is not perfect, as evidenced by the October 1987 stock market crash, when traders and institutions learned that even with Black-Scholes techniques deployed, when the market is crashing and no one is willing to buy, it's impossible to sell short. The outcome? On "Black Monday," the Dow Jones Industrial Average plunged 508 points or 22.6% on October 19, 1987.

There has been considerable debate about the role of momentum in sports. In a landmark study, Thomas Gilovich and several colleagues provided evidence that the "hot hand" in basketball was nothing more than a myth. Since then, there has been considerable research suggesting that many of the old saws about sports are untrue, and a movement toward more enlightened analysis has emerged, best exemplified in Michael Lewis' book Moneyball.

In this weekend's Wall Street Journal, Allen St. John wonders about the idea of "momentum" heading into baseball's post-season.

He writes that "while much is often made about late-season momentum as a harbinger of playoff success, in reality the relationship between the two is small... The playoffs are truly a second season. Only once since the advent of the wild card has the team with the best regular-season mark (the 1998 Yankees) won the World Series."

So if your favorite team has limped into the post-season, don't worry about it! Occasionally, there are legitimate reasons to fret over lost momentum. If a team has experienced a disastrous September because of injuries to its top starters, that will be a problem heading into the post-season -- not because of momentum, but because the pitchers are likely to remain unavailable!

I would argue that investors should look at the stock market the same way. Rather than buying into the idea of "momentum" in the stock market (I've seen no evidence that such a phenomenon really exists), think about factors that actually effect the business. Leave the cliches about "fighting the tape" and "moving averages" to the old wives.