Annual Report of the Directors of Research
    Published Date 
  
  
    Copyright 1930
  
 
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      Copy CitationEdwin F. Gay and Wesley C. Mitchell, Annual Report of the Directors of Research, February 3, 1930 (NBER, 1930), https://www.nber.org/books-and-chapters/annual-report-directors-research-february-3-1930/annual-report-directors-research.
 
     
    