| Year | Value | | 2021 | 11.14980347313 | | 2020 | 11.133732816231 | | 2019 | 11.092223596246 | | 2018 | 11.107168493486 | | 2017 | 11.10205035607 | | 2016 | 11.086790723396 | | 2015 | 11.060340040331 | | 2014 | 11.022408331726 | | 2013 | 11.015376067135 | | 2012 | 10.986335213978 | | 2011 | 10.943662905447 | | 2010 | 10.900485774524 | | 2009 | 10.866338046692 | | 2008 | 10.817045110813 | | 2007 | 10.81738678056 | | 2006 | 10.785734065099 | | 2005 | 10.735150677851 | | 2004 | 10.688751071213 | | 2003 | 10.678337097379 | | 2002 | 10.603511173907 | | 2001 | 10.587732290444 | | 2000 | 10.567155607406 | | 1999 | 10.602869982192 | | 1998 | 10.582692476155 | | 1997 | 10.576581133382 | | 1996 | 10.536694135326 | | 1995 | 10.541515435809 | | 1994 | 10.518840610158 | | 1993 | 10.544172501981 | | 1992 | 10.553452784293 | | 1991 | 10.623063432187 | | 1990 | 10.590519358761 | | 1989 | 10.573606789283 | | 1988 | 10.548786243848 | | 1987 | 10.547772006618 | | 1986 | 10.508703091222 | | 1985 | 10.508406250666 | | 1984 | 10.34360800616 | | 1983 | 10.181256144793 | | 1982 | 10.11661229685 | | 1981 | 9.995892725221 | | 1980 | 9.9689727656945 | | 1979 | 9.9526181538477 | | 1978 | 9.88943134834 | | 1977 | 9.8073449046299 | | 1976 | 9.7516403951796 | | 1975 | 9.6929769540893 | | 1974 | 9.6742724626906 | | 1973 | 9.6492216822031 | | 1972 | 9.5938113619016 | | 1971 | 9.5210145178917 | | 1970 | 9.5101113944101 | | 1969 | 9.5047954362848 | | 1968 | 9.4954501713277 | | 1967 | 9.4500654668132 | | 1966 | 9.4130617797886 | | 1965 | 9.3787089986129 | | 1964 | 9.3294481728709 | | 1963 | 9.2856326440232 | | 1962 | 9.2189838375513 | | 1961 | 9.1782797144604 |
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