How Well Can We Predict Our Own Survivability?

Having recently had my own brush with death, I was fascinated by one of the articles in the latest issue of the Vienna Yearbook of Population Research (Volume 14--2106) published by the Vienna Institute of Demography. Well, actually, they are all good articles, but the one by Alberto Palloni and Beatriz Novak caught my eye for two reasons: (1) Professor Palloni is a Past President of the Population Association of America (click here for an interview with him), and (2) we humans tend to be very interested in our potential ability to evaluate our own likely age at death.

In their research, Palloni and Novak compared people's own subjective responses about their probability of surviving to a particular age, with life table probabilities based on calculations from death certificate analysis at the national level. Their source of data for people's subjective probabilities was a set of questions asked in the Health and Retirement Study (HRS), funded over many years by the National Institutes of Health.

The HRS is a longitudinal survey designed to gather information on individuals in the U.S. from pre-retirement into retirement. The first wave’s (1992) target population included individuals born between 1931 and 1941 who were living in households, and the spouses or partners of these individuals, regardless of their ages. Out of the 15,497 individuals who were eligible to be interviewed in 1992, 12,654 respondents were actually interviewed. Since then, the individuals in this initial cohort have been re-interviewed every two years. The entire survey consists of five birth cohorts who have been incorporated into the study over time. In the present study, we examine data from the first, fourth, and fifth HRS cohorts.

Here's what they found:

We show that the subjective probabilities are remarkably close to the results of actual life tables constructed from observed data, that whites underestimate their survival chances more than blacks, that women underestimate their survival chances more than men, and that the subjective underestimation of conditional survival increases with age in all population subgroups. We find significant differences in the survival outlooks of the original HRS cohort and a more recent HRS cohort (1992 versus 2004). These differences persist after introducing suitable controls. The observed mortality differentials between smokers and non-smokers, obese and non-obese individuals, and high-education and low-education groups are quite close to those of these subgroups’ subjective survival expectations. Finally, we find large updating effects that result from recent health shocks on subjective expectations.

As the authors note, this is really an extension of the literature showing that self-rated health generally comes very close to what physicians would say about you in a physical exam. We tend to know ourselves pretty well, and tend to monitor our likely chances of survival in a reasonably realistic way.