Source: Federal Reserve Bulletin, April 1928, Pp. 234-235, And Successive Issues Through February 1930
This NBER data series m06011 appears on the NBER website in Chapter 6 at http://www.nber.org/databases/macrohistory/contents/chapter06.html.
NBER Indicator: m06011
Release: NBER Macrohistory Database
National Bureau of Economic Research, Sales of Retail Chain Stores, Drug Chains for United States [M06011USM331SNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M06011USM331SNBR/, September 2, 2015.