Data Are For Monthly Averages Of The Weekly Yields Index Given In "The Weekly Bond Buyer For The Capital Market Investor", Published By The Bond Buyer, New York City. Source: U.S. Bureau Of The Census, Business Cycle Developments, July 1964 And Subsequent Issues.
This NBER data series m13050 appears on the NBER website in Chapter 13 at http://www.nber.org/databases/macrohistory/contents/chapter13.html.
NBER Indicator: m13050
Release: NBER Macrohistory Database
National Bureau of Economic Research, Yields On Municipal Bonds, Twenty Bond Average for United States [M13050USM156NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M13050USM156NNBR, February 7, 2016.