Data Refer To Baa Grade Bonds. Source: Moody'S Public Utility Manual, 1965; Moody'S Bond Survey, Weekly Issues Thereafter.
This NBER data series m13064 appears on the NBER website in Chapter 13 at http://www.nber.org/databases/macrohistory/contents/chapter13.html.
NBER Indicator: m13064
Release: NBER Macrohistory Database
National Bureau of Economic Research, Yields On Public Utility Bonds, Lowest Rating for United States [M13064USM156NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M13064USM156NNBR/, July 30, 2015.