Data Are For All Bonds Having At Least Ten Years Maturity, Based On Arithemetic Average Yields. Data For December 1914 Were Obtained By A Linear Interpolation Between July And December. Source: F.R. Macaulay, The Movement Of Interest Rates, Bond Yields, And Stock Prices In The United States Since 1856 (NBER, 1938), Appendix Table 10, Col. 4, P. A142 And Following Pages.
This NBER data series m13019a appears on the NBER website in Chapter 13 at http://www.nber.org/databases/macrohistory/contents/chapter13.html.
NBER Indicator: m13019a
Release: NBER Macrohistory Database
National Bureau of Economic Research, Railroad Bond Yields Index for United States [M1319AUSM156NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M1319AUSM156NNBR/, October 9, 2015.