# year value 1901 15.3052 1902 14.69029 1903 14.54849 1904 14.30793 1905 13.83823 1906 14.351 1907 14.28572 1908 14.33011 1909 14.24486 1910 14.64121 1911 14.42225 1912 14.62599 1913 14.83031 1914 14.86703 1915 14.74931 1916 14.80842 1917 14.58434 1918 14.50216 1919 14.53295 1920 14.77035 1921 14.71829 1922 14.73726 1923 14.03062 1924 14.26229 1925 14.37248 1926 14.67146 1927 14.83747 1928 14.83875 1929 14.44562 1930 14.63931 1931 14.07448 1932 14.70034 1933 14.68069 1934 14.14461 1935 14.04744 1936 14.44498 1937 14.67786 1938 14.99688 1939 14.06653 1940 14.45387 1941 14.24638 1942 14.80708 1943 14.3665 1944 15.47797 1945 14.88757 1946 14.50836 1947 14.59479 1948 14.54801 1949 14.47698 1950 14.02768 1951 14.67163 1952 14.39256 1953 14.41145 1954 14.49617 1955 14.38363 1956 14.14388 1957 14.60293 1958 14.66471 1959 14.85981 1960 14.58071 1961 15.24932 1962 15.04513 1963 14.41538 1964 14.14906 1965 15.12887 1966 14.40903 1967 15.17815 1968 14.68011 1969 14.54718 1970 14.58402 1971 14.84719 1972 14.84228 1973 14.63397 1974 14.2415 1975 14.7053 1976 14.21998 1977 15.37447 1978 14.76309 1979 14.58829 1980 15.25571 1981 14.98407 1982 15.17503 1983 15.1556 1984 14.85329 1985 15.1137 1986 14.6751 1987 15.07362 1988 15.18189 1989 15.03998 1990 15.35043 1991 15.06635 1992 14.18004 1993 14.85082 1994 15.11984 1995 15.05751 1996 15.16624 1997 15.12809 1998 15.07318 1999 15.35952 2000 14.91172 2001 14.84315 2002 15.38017 2003 15.12944 2004 15.26515 2005 15.08502 2006 15.81433 2007 15.55491 2008 15.61724 2009 15.24401 2010 14.98422 2011 15.61755 2012 15.7943 2013 15.52937 2014 16.11341 2015 15.26497 2016 15.05501 2017 15.67069 2018 15.49658