Your friends know you better than you know yourself. They even know how long you've got to live. Well, roughly speaking they do.
It's not that they've got extrasensory perception, time machines, or membership in the secret conspiracy that surrounds you. It's just that psychological traits like conscientiousness and emotional stability are decent predictors of longevity, and your friends' beliefs about your traits are, when averaged, more reliable than your own.
Researchers know that personality traits affect health — conscientiousness, for example, turns out to be a pretty good predictor for risk of death. But the studies linking personality, health, and mortality are limited because they rely on participants' assessments of their own personalities. Apart from the bias that might introduce, it's also privy to external factors which could sway the participant — say, the weather that day. Fixing this validity problem would take a study in which researchers asked someone else — preferably friends, who see one another in a variety of situations — about individuals' personalities.
That's just what Joshua Jackson and colleagues did with the long-running Kelly Longitudinal Study, which began as an assessment of 300 young married couples in mid-1930s Connecticut. As part of the study, the late psychologist E. Lowell Kelly asked three to eight of each couples' friends to answer a series of questions Kelly had constructed to probe personality.
Analyzing Kelly's data in conjunction with death records — or confirmation that the original participants were still alive — for all but seven of the women, Jackson and team found that men viewed by their friends as more conscientious and open tended to live longer. The most conscientious men, for example, had about a 30 percent lower mortality risk compared with the average male participant. Similarly, the researchers estimated that women viewed as the most emotionally stable and the most agreeable had a 15 percent lower mortality risk.
Friends' ratings were better than the individuals' own assessments as well. Men's self-reports of conscientiousness and openness were still related to mortality, and the effect was weaker. There were no such connections for women.
Much of the predictive value from friends' ratings is because they were friends, the authors argue in Psychological Science. Single-friend ratings were, like self-reports, not particularly useful indicators of lifespan. "These analyses indicate that the superiority of peer ratings was due largely to the aggregation of ratings from multiple peers, which averaged out idiosyncratic tendencies of particular raters," the authors write.
Before you go asking your pals about your personality, the authors note, it's worth keeping in mind that Kelly's 300 couples were not exactly representative of the United States of the time, let alone the modern world. Those 600 people were predominantly white, middle class, and well educated — not to mention they were in their mid twenties in 1935.
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