# year value 1901 14.13881 1902 14.49321 1903 13.84908 1904 14.2401 1905 14.00078 1906 14.28154 1907 13.61224 1908 13.69673 1909 13.68641 1910 13.85302 1911 13.66857 1912 14.11927 1913 14.11166 1914 14.19001 1915 13.76809 1916 14.28733 1917 13.58768 1918 14.01026 1919 14.67166 1920 14.19361 1921 14.44457 1922 14.2066 1923 14.31355 1924 13.47965 1925 14.00398 1926 13.90967 1927 13.9827 1928 14.02425 1929 13.95763 1930 14.39932 1931 13.46475 1932 14.18234 1933 14.20684 1934 14.1227 1935 14.28474 1936 13.90219 1937 13.94664 1938 14.36198 1939 13.97928 1940 13.89934 1941 13.51751 1942 13.84921 1943 14.06155 1944 13.89046 1945 14.45861 1946 13.83415 1947 14.12846 1948 13.66056 1949 13.88095 1950 14.40098 1951 14.17268 1952 14.25698 1953 14.55246 1954 14.04953 1955 13.80698 1956 13.45842 1957 14.52143 1958 14.40423 1959 13.75887 1960 13.93794 1961 14.20285 1962 14.32552 1963 14.17243 1964 13.93725 1965 13.87351 1966 14.41267 1967 14.60809 1968 14.10464 1969 14.28403 1970 14.40978 1971 14.00603 1972 14.23381 1973 14.37491 1974 14.56391 1975 14.29088 1976 13.81899 1977 14.14401 1978 14.68784 1979 14.26026 1980 14.98428 1981 14.80925 1982 14.76389 1983 14.43166 1984 13.84834 1985 14.47592 1986 14.46456 1987 14.3201 1988 14.40644 1989 14.66294 1990 14.40688 1991 14.8808 1992 14.45322 1993 14.59303 1994 14.72024 1995 14.17089 1996 14.56072 1997 14.63251 1998 14.736 1999 14.42963 2000 14.2789 2001 14.2525 2002 14.58164 2003 14.71433 2004 14.49619 2005 14.60966 2006 14.08805 2007 14.61038 2008 14.56418 2009 15.11479 2010 14.89092 2011 14.56046 2012 14.64196 2013 14.92779 2014 14.6915 2015 15.09367 2016 14.87224 2017 15.016 2018 15.35267