No one knows his final score on the biggest and most important test of all.

I call it the Living Test, the unwritten exam that shows how many years we'll manage to squeeze out of our lives.   Some will squeeze out more, some less. But life expectancy is worth getting competitive about.

While much of the score is in our genes and gender at birth, choices we make can increase or decrease how many years we live. They may also determine whether we have the health to enjoy those years.

The Living Test is more important than any wealth score. It gives us an idea of how much life we may "leave on the table" by chance or negligence.

We can measure this by looking at the statistics of life expectancy in a slightly odd way. One of the most common population number sets is called a "Life Table." It shows the long trail of losses from birth to age 100, expressed as the number surviving from year to year. Beginning with an original group of 100,000 people, the table shows that 83,789 live to begin their 65th year and 82,607 finish it.

I hope to be among the 82,607---. my 65th birthday is in November.

It also shows that 52,178 of the original 100,000 begin their 81st year but only 49,173 finish it, making it the median year of life. From there, the attrition continues until only 2,851 of the original 100,000 begin their 100th year and 2,095 finish it.

As we all know, no one gets out alive. While life expectancy in America, broadly speaking, was 77.3 years in 2002, the brute fact is that many don't live that long. Many others, however, live much longer.

If you think of it as a kind of achievement test where we rank lives from the longest to the shortest, here is what the percentile scores would look like:

•  The top 2 percent live to be over 100.

•  The top 10 percent live to their 94th year or longer.

•  The top 25 percent live to their 89th year or longer.

•  The top 50 percent live to their 81st year or longer.

•  The bottom 25 percent live only to their 71st year.

•  The bottom 10 percent live only to their 57th year.

•  The bottom 1 percent live only to their 16th   year.

From this perspective, a romantic death at an early age--- the whole Keats, Baudelaire, Jim Morrison, Janis Joplin trip that many of us fantasized about at 18--- looks like what it is, a disastrous underachievement. It also puts a new light on the waste of early death.

So let's ask a tough question: Can we do anything to reach a higher percentile on the Life Table?

Yes.

The life expectancy tests on the Web may have different specific results, but every one of them shows gains in life expectancy if we take steps to preserve our health.   If you are a smoker and stop smoking, start exercising, and make an effort to have a better diet that will help you avoid obesity, you can add literal years to your life.

How many?

It all depends. Using the www.agingresearch.org calculator, for instance, I learned that changes I have made since turning 30--- when I quit smoking two packs of Camels a day, added moderate exercise, and started paying attention to diet--- have increased my life expectancy from 72.8 years to 86.8 years.

That's an increase of 14 years.

Does 14 years of additional life get your attention? It certainly gets mine.

Measuring the improvement on the Life Table shows a move from the bottom 28 percent to the top 33 percent.

And, trust me, there's still room for improvement.

In my case, family history pretty much rules out being in the top 1 percent. But getting to the top 25 percent---those who live to 89 or longer--- is only a matter of taking life seriously.

For a priceless gift, that's a small price to pay.

On the web:

Life Expectancy Calculator

United States Life Tables, 2002