Appendix F: Tables on Years of School Completed for Engineers, 1940, and Age and Years of School Completed for Engineers and Scientists, 1950

David M. Blank and George J. Stigler, The Demand and Supply of Scientific Personnel (NBER, 1957), https://www.nber.org/books-and-chapters/demand-and-supply-scientific-personnel/appendix-f-tables-years-school-completed-engineers-1940-and-age-and-years-school-completed-engineers.