Source: Bureau Of Labor Statistics, For 1919-1930 Data: Bulletin No. 610; For 1931-1934 Data: Mimeographed Release Of September 1938; For 1935-1939: Mimeographed Report Of May 1940; For 1940-1942:"Employment And Payrolls" And Monthly Labor Review.
This NBER data series m08144 appears on the NBER website in Chapter 8 at http://www.nber.org/databases/macrohistory/contents/chapter08.html.
NBER Indicator: m08144
Release: NBER Macrohistory Database
National Bureau of Economic Research, Index of Factory Employment, Automobiles for United States [M08144USM331NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M08144USM331NNBR/, July 6, 2015.