Year | Value | 2021 | 18.74769426837 | 2020 | 18.74769426837 | 2019 | 18.74769426837 | 2018 | 18.74769426837 | 2017 | 18.74769426837 | 2016 | 18.74769426837 | 2015 | 18.74769426837 | 2014 | 18.74769426837 | 2013 | 18.74769426837 | 2012 | 18.714156353758 | 2011 | 18.278163463796 | 2010 | 17.775094744609 | 2009 | 18.445853036858 | 2008 | 18.278163463796 | 2007 | 17.741556829996 | 2006 | 17.288794982728 | 2005 | 16.785726263541 | 2004 | 17.171412281584 | 2003 | 16.668343562397 | 2002 | 16.550960861254 | 2001 | 16.715296642855 | 2000 | 16.882986215917 | 1999 | 17.054029580441 | 1998 | 17.221719153503 | 1997 | 17.389408726565 | 1996 | 17.557098299628 | 1995 | 17.72478787269 | 1994 | 17.892477445752 | 1993 | 18.060167018815 | 1992 | 18.227856591877 | 1991 | 18.402253747862 | 1990 | 18.378777207633 | 1989 | 18.311701378408 | 1988 | 18.244625549183 | 1987 | 18.177549719958 | 1986 | 18.110473890733 | 1985 | 17.942784317671 | 1984 | 17.708018915384 | 1983 | 17.640943086159 | 1982 | 17.573867256934 | 1981 | 17.506791427709 | 1980 | 17.533621759399 | 1979 | 17.439715598484 | 1978 | 17.272026025422 | 1977 | 17.104336452359 | 1976 | 16.768957306235 | 1975 | 16.265888587048 | 1974 | 16.097119286361 | 1973 | 15.927304429467 | 1972 | 15.758063434587 | 1971 | 15.570307785154 | 1970 | 15.657480050962 | 1969 | 15.758063434587 | 1968 | 15.858646818212 | 1967 | 15.959230201837 | 1966 | 16.093341380004 | 1965 | 16.160396969087 | 1964 | 16.227452558171 | 1963 | 16.294508147254 | 1962 | 16.361563736337 | 1961 | 16.431972104875 |
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