A story in the New York Times, “The Island Where People Forget to Die,” marvels at how the population (673 souls) of Ikaria, a Greek island in the Aegean, seem to live for a long time.
The story refers to research by two scholars, Gianni Pes of the University of Sassari in Italy and Michel Poulain of Belgium, who have conducted anecdotal research on population clusters with a disproportionate number of people who live a long time. Their list of anomalous communities is comprised, in addition to Ikaria, of:
- “on Costa Rica’s Nicoya Peninsula, we discovered a population of 100,000 mestizos with a lower-than-normal rate of middle-age mortality.”
- “in Loma Linda, Calif., we identified a population of Seventh-day Adventists in which most of the adherents’ life expectancy exceeded the American average by about a decade.”
- “a region of Sardinia’s Nuoro province as the place with the highest concentration of male centenarians in the world.”
For Ikaria, people tend to live a long time, and the protaganist of the story moved there after being diagnosed with cancer in 1976, but it went into remission and he is still alive. Bless him.
Do you see the problem here? If one slices and dices the world population of seven billion enough ways—the cited researchers’ clusters include one ethnic group, a religious group, a regional group, and an island—then one will find outliers. Similarly, if one adopts enough different measures of longevity—in this case, middle-age mortality, life expectancy, prevalence of centenarians, and, in Ikaria, rates of people who reach 90—then one will surely find a few that emerge as outliers. (Not to mention the small sample size in this case.)
Out of the practically infinite number of semi-coherent groupings of people and semi-coherent measures of longevity, by definition, there will be a few that fall into the 0.01%, or 0.0001%, tail of the distribution. It’s as if you toss a coin 1,000,000 times and search the results for a string of ten consecutive heads and, finding it, you say, “ah-ha—this coin is biased!” In fact, you expect to get ten consecutive heads about once in every 1,000 ten-toss experiments.
We can hope that Drs. Pes and Poulain consider this inferential reality in their research, but the article does not even address this obvious potential rejoinder.
By the way, the article cites several plausible reasons for longevity in Ikaria: the island’s hot springs; the relaxed lifestyle there*; a sense of community; a healthy diet, including vegetables, wine, and olive oil; exercise, since the area is rural and hilly; and the popular local drink of tea made from local herbs. These factors make Ikaria seem like a nice place to live — and no doubt these factors contribute at a basic level to longevity—but they are hardly so novel as to paint this case study as extraordinary.
*Unemployment on the island is 40%.