American scientists say they've developed a way of predicting how likely a person is to live beyond the age of 100.
The method, described in the journal Science, is based on the largest study of centenarians in the world, which identified 150 genetic "signposts" in exceptionally long-lived people.
The researchers created a mathematical model that takes information from these signposts to work out a person's chance of reaching 100.
Only one in every 6000 people in industrialised countries reaches 100 - and 90% of them are still disability-free by the age of 93.
The BBC reports that the research was led by Paola Sebastiani, a professor of biostatistics at Boston University, and Thomas Perls, associate professor of medicine at the same university.
"We tested our model in an independent set of centenarians and achieved an accuracy of 77%," says Professor Sebastiani. "So out of 100 centenarians we could correctly predict the outcome of 77."
She says that the "23% error rate" indicates that, although "genetics is fundamental in exceptional longevity it's not the only thing".
"So there may be other factors like environment or other lifestyles that may help people live longer and healthier lives."
Adventist Church study indicators
Professor Perls says a previous study had looked at longevity in a group of people belonging to the Seventh-day Adventist Church.
"Those individuals have probably among the highest average life expectancy that we know of in the US of 88 years," he says.
"What makes these people live a very long life is not a lack of genetic predisposition to diseases, but rather an enrichment of longevity.
"They get there by virtue of the fact that they have a religion that asks them to be vegetarian, they regularly exercise, they don't drink alcohol, they tend to manage their stress well through religion and time with family and they don't smoke.
"To live the additional 10-15 years beyond the age of 88, our paper is indicating that genetics are playing an increasingly important role."
Professor Perls says a simple test could be developed to screen people's chances of being so long-lived. There are already plans for a free-to-use website where people will be able to use the mathematical model to work out their chances of exceptional longevity.