# year    value 
 1940 23.18296 
 1941 23.23275 
 1942  23.2548 
 1943 23.00432 
 1944 23.24819 
 1945 23.17154 
 1946 23.06963 
 1947 23.08765 
 1948 23.06265 
 1949 22.96736 
 1950 22.84929 
 1951 22.91901 
 1952 23.06056 
 1953 23.03591 
 1954 22.95909 
 1955 22.85272 
 1956 22.61645 
 1957 23.12001 
 1958 23.31692 
 1959 23.22463 
 1960 22.94255 
 1961 23.24075 
 1962 23.06312 
 1963 23.13767 
 1964 22.99442 
 1965 23.13223 
 1966 23.14781 
 1967 23.07131 
 1968 22.90944 
 1969 23.40573 
 1970 23.29663 
 1971 22.86336 
 1972 23.20934 
 1973 23.32203 
 1974 22.65896 
 1975 22.82986 
 1976 22.68453 
 1977 23.13918 
 1978 23.00414 
 1979 23.16948 
 1980 23.30768 
 1981  23.0904 
 1982 23.16178 
 1983 23.50453 
 1984 23.10991 
 1985 23.20177 
 1986 23.28917 
 1987 23.57828 
 1988 23.45948 
 1989 23.10539 
 1990 23.40453 
 1991 23.40532 
 1992 23.37529 
 1993 23.38954 
 1994 23.40947 
 1995 23.53012 
 1996 23.37146 
 1997 23.51535 
 1998 23.86832 
 1999 23.34989 
 2000 23.23725 
 2001 23.42206 
 2002 23.71126 
 2003 23.69871 
 2004 23.59227 
 2005 23.85622 
 2006 23.54426 
 2007 23.54071 
 2008 23.42887 
 2009 23.67129 
 2010 23.68294 
 2011 23.36445 
 2012 23.54401 
 2013 23.70547 
 2014 23.75252 
 2015 23.92263 
 2016 23.92691 
 2017 23.84805 
 2018 23.71343