"In 1958, corporations listed in the S&P 500 had an average stay of 61 years. By 1980, numbers from research firm Innosight reveal that the average stay had declined sharply to 25 years. In 2011, the average tenure dropped to 18 years. At the present rate of churn, Innosight’s research estimates three-quarters of today’s S&P 500 will be replaced by 2027."
