The Figures Here Are A Geometric Average. Source: Frickey, Review Of Economic Statistics, August, 1921, Pp.255-257; June, 1923 Supplement (Statistical Record, 1922) P.169.
This NBER data series m11008 appears on the NBER website in Chapter 11 at http://www.nber.org/databases/macrohistory/contents/chapter11.html.
NBER Indicator: m11008
Release: NBER Macrohistory Database
National Bureau of Economic Research, Index of Preferred Stock Prices, New York Stock Exchange for United States [M11008USM322NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M11008USM322NNBR, February 8, 2016.