# year value 1901 16.11315 1902 15.94738 1903 15.28844 1904 15.54705 1905 15.50935 1906 15.59478 1907 15.39557 1908 15.50296 1909 15.41177 1910 14.97057 1911 15.44085 1912 15.62158 1913 16.21345 1914 16.02893 1915 15.64379 1916 15.81552 1917 15.92152 1918 15.75922 1919 16.17299 1920 15.96014 1921 15.27277 1922 15.34446 1923 15.80146 1924 15.59462 1925 15.42439 1926 15.81838 1927 15.75376 1928 15.16707 1929 15.63164 1930 15.64906 1931 15.67185 1932 15.83281 1933 15.34 1934 15.19685 1935 15.54802 1936 15.35861 1937 15.31341 1938 15.5298 1939 15.71109 1940 15.66091 1941 15.4144 1942 15.8004 1943 15.96641 1944 16.03256 1945 16.24023 1946 15.49703 1947 15.55504 1948 15.40623 1949 15.68868 1950 15.68472 1951 15.28255 1952 16.14457 1953 16.0094 1954 15.85374 1955 15.85635 1956 15.13013 1957 15.95001 1958 15.67702 1959 15.58662 1960 16.41035 1961 15.6165 1962 15.82443 1963 16.0919 1964 15.59045 1965 15.60568 1966 15.19069 1967 15.37493 1968 15.9887 1969 15.81708 1970 16.16284 1971 14.94915 1972 15.48522 1973 16.00282 1974 15.4563 1975 15.80448 1976 15.34858 1977 15.62465 1978 16.21301 1979 16.3783 1980 16.18629 1981 16.2278 1982 16.14221 1983 16.23164 1984 16.08348 1985 15.90658 1986 15.87361 1987 16.43931 1988 16.10258 1989 16.34813 1990 16.27555 1991 16.24883 1992 15.49946 1993 15.93858 1994 15.94588 1995 16.01084 1996 15.90461 1997 15.61855 1998 16.18066 1999 16.74747 2000 15.66651 2001 16.14017 2002 16.18429 2003 16.20623 2004 16.35703 2005 16.46718 2006 16.51946 2007 16.08352 2008 16.67603 2009 16.72185 2010 16.02168 2011 16.28994 2012 16.59911 2013 16.60587 2014 16.58317 2015 16.41647 2016 16.89702 2017 17.00825 2018 17.08826