| Year | Value | | 2021 | 11.114428374456 | | 2020 | 11.152398670327 | | 2019 | 10.076130732815 | | 2018 | 10.169061165736 | | 2017 | 10.149836683901 | | 2016 | 9.8697653431959 | | 2015 | 10.09416287238 | | 2014 | 9.5042543022813 | | 2013 | 9.6907462671389 | | 2012 | 9.7316036997581 | | 2011 | 9.4497464692901 | | 2010 | 9.449510990068 | | 2009 | 9.4470090994745 | | 2008 | 9.4306655459558 | | 2007 | 9.3508116748212 | | 2006 | 9.2589114432609 | | 2005 | 9.4609605110208 | | 2004 | 9.2567853233677 | | 2003 | 9.7855670555447 | | 2002 | 9.5797487349088 | | 2001 | 9.5036850872136 | | 2000 | 9.6263518333689 | | 1999 | 9.7673878340427 | | 1998 | 9.8060042055991 | | 1997 | 9.7397547146304 | | 1996 | 9.8380123537458 | | 1995 | 9.8611902277713 | | 1994 | 9.8355753167814 | | 1993 | 9.9706992396585 | | 1992 | 9.8484904105528 | | 1991 | 10.006320549864 | | 1990 | 10.022995652226 | | 1989 | 9.9370871533097 | | 1988 | 9.9331166412607 | | 1987 | 9.938631909064 | | 1986 | 10.097181389245 | | 1985 | 10.220775805802 | | 1984 | 10.079540853058 | | 1983 | 10.290699124591 | | 1982 | 10.082306772181 | | 1981 | 10.255379326771 | | 1980 | 10.298582260986 | | 1979 | 10.206084856372 | | 1978 | 10.321295463243 | | 1977 | 10.268837041656 | | 1976 | 10.51074856007 | | 1975 | 10.612625015637 | | 1974 | 10.430498609254 | | 1973 | 10.553941591747 | | 1972 | 10.493284680276 | | 1971 | 10.634771103013 | | 1970 | 10.621402635639 | | 1969 | 10.879726353259 | | 1968 | 10.710279062123 | | 1967 | 10.398668507869 | | 1966 | 10.364284480125 | | 1965 | 10.501774171128 | | 1964 | 10.273077754448 | | 1963 | 10.594207145789 | | 1962 | 10.568767578819 | | 1961 | 10.237928347975 | | 1960 | 10.483328475698 |
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