PEOPLE WHO lived centuries ago may have had much longer lives than is commonly supposed, due to a potentially devastating flaw in archaeologists' standard methods.

Measures used by scientists such as the wear on bones and teeth, and the development of skeletal characteristics, do not match closely enough to our actual age to offer precise data about age - and can often underestimate it, according to new research led by Mark Pollard, professor of archaeological sciences at the University of Bradford.

His team's work, with the University of Leeds, suggested that age studies of bones from people who lived around the 11th century could have been up to 30 years too low - contradicting the assumption that hardly anybody then survived beyond the age of 55. Instead, they might have survived into old age. The work, reported in today's New Scientist, would overturn years of work by archaeologists, including both the methods of data-gathering, the data itself and any conclusions about such peoples' lifestyles based on that data.

"We think we have shown problems in the way that age estimates are obtained," said Professor Pollard. "But we are not convinced that we have the solution to that yet. Still, that is a step forward."

The team's criticism of standard methods rests on the statistical technique used to estimate the biological ages of bones. Called "regression", it groups large samples of bones of known ages and produces a plot which best fits the scattered points.

But, said Professor Pollard, people can differ enough that such measures become inaccurate. "Individuals don't respond to ageing in the same way; what we really need are skeletal ageing data that are better matched to peoples' ages." The present systems, such as the length of bones, and the degree of wear at joints and in teeth, is too imprecise to stand rigorous statistical examination.