Overlapping Quarters (Second,1921 And Second,1923) Were Averaged To Allow Continuous Cumulation. Source: Data For 1920-1947: G.H. Moore, Business Cycle Indicators, Vol. 2, NBER, P. 159-160; Data For 1948-1965: U.S. Bureau Of The Census, Business Cycle Developments, October 1964 And Subsequent Issues
This NBER data series q16046 appears on the NBER website in Chapter 16 at http://www.nber.org/databases/macrohistory/contents/chapter16.html.
NBER Indicator: q16046
Release: NBER Macrohistory Database
National Bureau of Economic Research, Cumulated Net Diffusion Index, Profits of 17-700 Manufacturing Corporations, One Quarter Span for United States [Q16046USQ272SNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/Q16046USQ272SNBR, May 30, 2016.