For instance, optimistic people have a tendency to ignore details, meaning they don't follow doctor's orders correctly or lead themselves into unhealthy situations or addictions. It was the conscientious people—careful, sometimes even neurotic, but not catastrophizing—who lived longer, write Friedman and Martin, researchers at the University of California, Riverside. And, their studies show, some of what we think will benefit our children may actually rob them of years later in life. In the Terman study, precocious, active children who were sent to school a year early, as Philip was, tended to have emotional problems that led to unhealthy behaviors and shortened life span.

The list of findings goes on and on, and what emerges is that each individual, like Philip, has a constellation of behaviors and experiences that determine the quality and the quantity of their life. Though some of them are not under our control—did your parents divorce? Too bad for you!—others, like finding a community of friends who need your help and can help you, are eminently achievable. I spoke with Dr. Friedman about what we can learn from The Longevity Project.

Most psychological studies collect data from small groups of subjects over relatively short periods of time. How is working with this giant trove of information different?

An 80-year rich archive on so many people is simply unprecedented. After we discover some important correlation—say, women who are religious tend to live longer than nonreligious women—it allows us to return to the archive to do another study investigating the reasons for what we have found. (In that case, the added longevity turned out to be because of increased social interactions through a church, a benefit the nonreligious can reap too.)

For example, when we discovered that the people who were hard workers, accomplished, and successful lived the longest, we of course looked at what specific behaviors of successful people might contribute to health. But we were also able to look back and study what larger patterns in their lifestyles led these people to be both successful and long-lived. It can take a year or more to do each follow-up study, but we get a deep understanding that hasn't otherwise been possible.

This is what is thrilling to me—to go beyond the trivial. I don't really much care whether walnuts have more omega-3 fatty acids than pecans; I want to know which fundamental patterns of living lead to long, healthy lives.

You found that certain clusters of behaviors and personality traits relate to longevity. What were a few of the most counterintuitive connections you uncovered?

One of our longevity myths is "Get married, and you will live longer." The data tell a different story.

Marriage was health-promoting primarily for men who were well-suited to marriage and had a good marriage. For the rest, there were all kinds of complications.