@oristarA,
From looking at your link, it seems that Mr. Friedman and Mr. Martin conducted a 20 year study, which was inspired by earlier data obtained more than 80 years ago:
Quote:Friedman and Martin examined, refined and supplemented data gathered by the late Stanford University psychologist Louis Terman and subsequent researchers on more than 1,500 bright children who were about 10 years old when they were first studied in 1921. "Probably our most amazing finding was that personality characteristics and social relations from childhood can predict one's risk of dying decades later," Friedman concluded.
So, although poorly written, the article does suggest that Friedman and Martin conducted a 20 year study which culminated more than 80 years of
combined data review.