# year value 1901 15.01717 1902 14.74078 1903 14.49693 1904 14.6334 1905 14.34762 1906 14.77268 1907 14.44839 1908 14.57391 1909 14.39042 1910 14.71258 1911 14.45562 1912 14.90577 1913 15.03362 1914 15.10479 1915 14.86847 1916 14.74827 1917 14.67071 1918 14.77114 1919 15.08248 1920 14.85233 1921 14.89463 1922 14.71338 1923 14.62679 1924 14.32187 1925 14.56263 1926 14.82866 1927 14.76765 1928 14.68809 1929 14.66303 1930 15.00961 1931 14.34741 1932 14.86637 1933 14.7086 1934 14.73461 1935 14.63279 1936 14.67413 1937 14.70851 1938 14.85218 1939 14.76038 1940 14.81491 1941 14.59786 1942 14.75543 1943 14.67516 1944 15.00095 1945 15.05853 1946 14.57394 1947 14.83656 1948 14.64732 1949 14.66413 1950 14.81624 1951 14.93171 1952 14.77917 1953 14.87492 1954 14.72715 1955 14.51923 1956 14.38539 1957 14.90698 1958 14.90116 1959 14.87232 1960 14.82234 1961 15.13301 1962 15.07743 1963 14.89235 1964 14.4498 1965 15.04976 1966 14.68625 1967 15.04714 1968 14.95292 1969 15.0283 1970 14.94608 1971 14.76291 1972 15.05462 1973 14.99284 1974 14.83233 1975 15.0304 1976 14.58845 1977 15.27052 1978 15.0644 1979 15.2494 1980 15.44176 1981 15.29279 1982 15.32014 1983 15.20006 1984 14.62698 1985 15.29866 1986 15.0344 1987 15.19167 1988 15.22297 1989 15.32587 1990 15.29556 1991 15.29695 1992 14.78121 1993 15.17894 1994 15.40525 1995 14.98544 1996 15.11105 1997 15.36293 1998 15.36285 1999 15.36429 2000 15.085 2001 15.28293 2002 15.23877 2003 15.38747 2004 15.4213 2005 15.384 2006 15.46645 2007 15.26757 2008 15.48061 2009 15.65001 2010 15.31576 2011 15.49416 2012 15.53919 2013 15.78732 2014 15.80162 2015 15.68403 2016 15.55662 2017 15.8642 2018 15.7798