# year value 1940 20.03155 1941 20.074 1942 19.84415 1943 20.1099 1944 20.33989 1945 20.31876 1946 19.91101 1947 19.80573 1948 19.82989 1949 19.60266 1950 19.53835 1951 19.7351 1952 19.6155 1953 19.89098 1954 19.52882 1955 19.39505 1956 19.06128 1957 19.68446 1958 19.90827 1959 19.63285 1960 19.69573 1961 20.16465 1962 19.88622 1963 20.08225 1964 19.73731 1965 20.09772 1966 19.95892 1967 19.98046 1968 19.90998 1969 20.46299 1970 20.13386 1971 19.63266 1972 20.08723 1973 19.71513 1974 19.35284 1975 19.52142 1976 19.4327 1977 19.85554 1978 19.75984 1979 19.73411 1980 19.9629 1981 19.70309 1982 19.95358 1983 20.10446 1984 19.57122 1985 19.85999 1986 19.94643 1987 20.27297 1988 19.89423 1989 19.86916 1990 19.84993 1991 20.03533 1992 19.94382 1993 19.9648 1994 20.32873 1995 20.15625 1996 19.80836 1997 20.41166 1998 20.31798 1999 19.64775 2000 19.73729 2001 19.93387 2002 20.05278 2003 20.10545 2004 20.16056 2005 19.98792 2006 20.22546 2007 19.64512 2008 19.94315 2009 20.24658 2010 20.0948 2011 20.03436 2012 20.27954 2013 20.082 2014 20.33793 2015 20.64013 2016 20.3109 2017 20.41065 2018 20.08675