There once was a wise, old bookmaker who was approached by a neophyte who asked him about the meaning of life.

"Life?" the ancient oddsmaker replied. "Seven to five against."All life is risky. In fact, no one gets out alive. But how are we to set the course of our lives without knowing what the real risks are?

This is the point of "Living Against the Odds," a three-hour documentary special on PBS tonight (7 p.m., Ch. 7). It's a thorough and fascinating look at how we can benefit in our own lives from the dismal science of risk analysis.

What, you may ask, IS risk analysis? It's that science that tells you your chances of dying in the next five minutes are one in 12 million.

Feel better?

"Risk analysis is the process of converting science to numbers," said Baruch Fischhoff of Carnegie Mellon University, a professor of engineering and social policy. He studies how we perceive risks like terrorism and automobiles.

"With risk analysis, you can decide what your best buys are in risk protection," he said. "In our everyday language, we do talk about risks, but they really do vary tremendously. In order to make any decision, we've got to know how big it is, how confident we are about the size of the risk and if they're anything you can do about it."

The first segment examines the risks we face in our daily lives.

"Living Against the Odds" tells you the death rate for hang gliding is 114 per 100,000 participants annually, as opposed to 25 per 100,000 sky divers, 3 per 100,000 scuba divers and .002 deaths per 100,000 basketball players a year.

Remember the fear of terrorism that canceled trips to Europe in the '80s? The chance of being killed by a terrorist was one in 2 million; by contrast, the risk of death in an automobile is about 400 times higher, one chance in 5,000.

The second hour looks at those disasters of man and nature - earthquakes, plane crashes, floods and the rest - which are mostly beyond human control.

It spends time with the residents of the lovely, green city of Memphis, Tenn., on the Mississippi River, home of Elvis and the city nearest the epicenter of the next major earthquake involving the New Madrid fault.

Seismologists reckon that there's a 40 percent to 63 percent chance of a severe quake - a magnitude 6 on the Richter scale of ground motion - on the New Madrid fault in the next 15 years. In the next 50 years, some say, it's a lock.

The third hour - and perhaps the best - looks at the people of two cities who are coping with environmental risks.

The first city is Bytom, a grimy little industrial city in the Silesia region, that may be the most polluted place on Earth, threatening the health of everyone who lives there. And we see the people who are ill.

Poland's government, desperate for exports and hard currency, allowed the industrial pollution of air and water by state industry.

The second city is Braintree, Mass., where the residents fought the installation of a hazardous waste incinerator in their city.

The contrast between Braintree's rambunctious, activist neighbors fighting in a political process and Bytom's tragedy is stark.

"I went to Bytom," Fischhoff said. "I like to think we did them a real service in that . . . they actually get their story told."

"Living Against the Odds" tried to work on two levels, Fischhoff said. First, to show viewers the facts of risks, juxtaposed and compared with others. And second, to give people a general theory of risk to use in making decisions.