 Periodic collection of prices was started, and in 1919 the Bureau of Labor Statistics began publication of separate indexes for 32 cities.Regular publication of a national index, the U.S. city average began in 1921, and indexes were estimated back to 1913 using records of food prices.Because people's buying habits had changed substantially, a new study was made covering expenditures in the years 1934–1936, which provided the basis for a comprehensively revised index introduced in 1940.