My parents had an unspoken arrangement. My father looked on the bright side of life while my mother spotted the problems.

My graduation dinner was a classic example. The waiter seated us at a table with a terrific view of the men's room. My father never noticed anything negative. Why should he? He could count on my mother to complain.

My mother came through and got us moved to a better table. My mother also found it necessary to mention that the restaurant was too hot, the music was too loud, and the food was cold.

Unfortunately my mother died at 60; my father, thankfully, lived much longer.

The latest research, just published in 2009, found that optimism predicts longer life expectancy. In a new study, researchers at the University of Pittsburgh reviewed surveys of personality traits of more than 100,00 women aged 50 and over, participants in the Women's Health Initiative. They found a strong link between optimism and a person's risk for cancer, heart disease and early death.

More optimistic women, who looked on the bright side, were found to be 14 percent less likely to die from any cause, 30 percent less likely to die from heart disease, and 23 percent less likely to die from cancer. Optimists were also less likely to suffer from high blood pressure or diabetes and less likely to smoke cigarettes.

"Taking into account income, education, health behaviors, and whether or not you are physically active, whether or not you drink or smoke, we see optimists with a decreased risk of death compared to pessimists," says Dr. Hilary Trindle, lead author of the study and an assistant professor of medicine at the University of Pittsburgh.

"I was surprised that the relationship between optimism and longevity was independent of all those other factors."

Why does optimism have such protective functions? Possibly, optimistic people have a larger social network and more friends they can rely on in times of crisis because they are much more likable. They also tend to cope better with stress, a risk factor that has been associated previously with high blood pressure, heart disease, and early death.

Some people are born optimistic like my father, but optimism can also be learned.

A certain belief system is characteristic of optimistic people, finds professor of psychology, Martin Seligman, whose book "Learned Optimism" has defined the field.

Optimistic people believe that bad events:

• Are temporary setbacks and are isolated to particular circumstances.

• Can be overcome by effort and talent.

The pessimists react to setbacks with the idea that:

• Bad events will last a long time and there is nothing I can do about them.

• Will undermine everything I do.

• Are my fault.

If you interpret events in the pessimists' way, you suffer from "learned helplessness," finds Seligman, in studies of dogs exposed to noxious stimuli that they could not control. After a while, they stopped trying.

Pessimism, he finds, leads to depression, a psychological epidemic in the modern world. Some cases of depression are not biochemical and few are rooted in early childhood experiences. They have their origin in the explanatory style that leads to negativism.

People can change their explanatory style and move out of depression, a technique psychiatrists call "cognitive behavioral therapy."

Fundamentally, you argue against negative thoughts. If you're thinking, I've failed at this task," you learn to think "I've done well at a lot of other tasks and I have what it takes to do well in this one."

Women have twice the rate of depression as men, in part because they are more prone to ruminate, thinking about their failures over and over.

This is not to say that pessimism does not have its cheerful side. Pessimism makes us vigilant, so we are more likely to avoid bad investments and get into dangerous, risky situations.

Still, "smile and the world smiles with you, cry and you cry alone."