We all know that death is certain. What we don't know is when, at least we don't know yet. But Researchers at San Francisco Veterans Administration Medical Center in California have developed a test for those 50 years or older that can predict with 80 percent accuracy whether they will live another four years.

The test is based on a long-term study of 20,000 older adults. In a random sample interviewed by ABC-TV, one woman said she would definitely take the test. "I would want to know how much time I had left and to see if I had a shorter lifespan to see if there was anything I could do to prevent that," she said.

But others responded differently when asked. "I wouldn't take the test because I don't want to know. I'd rather be surprised," a man told the interviewer. An elderly woman responded, that she didn't want to know either because, she said, "I am living everyday like it were the last one anyway!"

The test evaluates such risk factors as age, sex, weight, tobacco use and medical conditions like diabetes, cancer and lung disease. The test also considers a person's ability to manage everyday chores like walking several blocks, bathing and handling money.

The lower the score, the better, says David Katz, associate professor at the Yale University School of Public Health. "If you get a very low score, you have less than a 4 percent chance of dying within four years," he says. "If you score very high on this test, your risk could be as high as almost 70 percent."

Dr. Katz says patients can lower their risk of death by making some lifestyle changes. "For example, one of them is do you smoke or not. You can stop if you do. Others relate to your level of fitness. Can you push an item across the room? Do you get winded walking a short distance?"

Dr. Katz recommends discussing test results with a caregiver who can help design an action plan that can lower your score and improve your health. The research is published in the Journal of the American Medical Association.