ISBN 0-385-51245-7. The Next100Years: A Forecast for the 21st Century(英语:The Next100Years: A Forecast for the 21st Century) [未来100年:对21世纪的预测]. Doubleday
(原始内容存档 (PDF)于2017-06-09) (英语). Mean years of schooling (of adults) (years) is a calculation of the average number of years of education received by people