Well, that is not actually true though you should be nice to your friends anyway, and to people in general for that matter. What a new study suggests is that your peers’ view of your personality is a better predictor of your mortality than your own view of yourself.

There have been many studies that have said hat having a positive attitude to life predicts a lower mortality rate. But these have depended on self-reports of personality. What a new study suggests is that your friends are likely to be more accurate in gauging your personality than you are.

Here’s the abstract of the paper reporting this effect that looked at a sample of white people from New England over a 75-year period.

Although self-rated personality traits predict mortality risk, no study has examined whether one’s friends can perceive personality characteristics that predict one’s mortality risk. Moreover, it is unclear whether observers’ reports (compared with self-reports) provide better or unique information concerning the personal characteristics that result in longer and healthier lives. To test whether friends’ reports of personality predict mortality risk, we used data from a 75-year longitudinal study (the Kelly/Connolly Longitudinal Study on Personality and Aging). In that study, 600 participants were observed beginning in 1935 through 1938, when they were in their mid-20s, and continuing through 2013. Male participants seen by their friends as more conscientious and open lived longer, whereas friend-rated emotional stability and agreeableness were protective for women. Friends’ ratings were better predictors of longevity than were self-reports of personality, in part because friends’ ratings could be aggregated to provide a more reliable assessment. Our findings demonstrate the utility of observers’ reports in the study of health and provide insights concerning the pathways by which personality traits influence health.

Why are peer reports better than self-reports? The text of the paper (paywall) explains.

Our findings indicate that the predictive advantage of peer reports results from the increased reliability achieved by averaging multiple peer reports, although we cannot rule out the possibility that peers can identify unique information that people might not see in themselves.

I found it interesting that being more conscientious and open was significant for men while emotional stability and agreeableness were significant for women. Why do they have different markers for mortality? The authors hazard an opinion that it is due to the role of women in earlier days, since the study tracked people beginning in 1938.

Predictors of mortality risk were different for women than for men; among women, only peer ratings, not self- ratings, were associated with mortality risk. These results must be interpreted within the historical context of this cohort, the members of which reached adulthood in the first few decades of the 20th century. Only a minority of female KCLS participants had an occupation other than being a housewife. It is likely that high levels of peer- rated emotional stability and agreeableness reduced mortality risk because they largely reflect positive characteristics indicative of a supportive and easy-going wife, such as the characteristics described in the social theory of the time.

I am not sure why the authors felt that they needed to explain why the women were different from the men rather than the other way around. It may be due to the fact that we tend in these kinds of sociological studies in the US to see white males as the norm and any variances from that norm are the ones that need explaining.