| Year | Value | | 2021 | 10.803114175241 | | 2020 | 10.557423346692 | | 2019 | 9.5449928945208 | | 2018 | 9.5674324903619 | | 2017 | 9.5060591806395 | | 2016 | 9.3304004344257 | | 2015 | 9.3866819119876 | | 2014 | 9.0708379343867 | | 2013 | 9.1280285474582 | | 2012 | 9.099437328824 | | 2011 | 8.9762513403234 | | 2010 | 8.9516377672859 | | 2009 | 8.8855043957071 | | 2008 | 9.0150660075229 | | 2007 | 8.9362509117658 | | 2006 | 8.8980497462826 | | 2005 | 9.0754107004361 | | 2004 | 8.9052051237695 | | 2003 | 9.1589440215056 | | 2002 | 9.0919429772399 | | 2001 | 9.0202920637833 | | 2000 | 9.0853798952965 | | 1999 | 9.203417199272 | | 1998 | 9.1492018911092 | | 1997 | 9.1811704453391 | | 1996 | 9.2505846665081 | | 1995 | 9.3237843994632 | | 1994 | 9.2254874579003 | | 1993 | 9.3206833418595 | | 1992 | 9.1116599045805 | | 1991 | 9.1153677543741 | | 1990 | 9.0907091444643 | | 1989 | 9.0581989803653 | | 1988 | 9.0858525143497 | | 1987 | 8.9719536928477 | | 1986 | 9.0523065452712 | | 1985 | 9.1789698785339 | | 1984 | 9.0784194839888 | | 1983 | 9.1468334307868 | | 1982 | 9.0096268213986 | | 1981 | 9.0931346601627 | | 1980 | 9.2429432734605 | | 1979 | 9.0520510228554 | | 1978 | 9.1412687757127 | | 1977 | 9.067409111151 | | 1976 | 9.2750559886238 | | 1975 | 9.2928883385426 | | 1974 | 9.3182615297447 | | 1973 | 9.4396754977131 | | 1972 | 9.3781232452997 | | 1971 | 9.4189545713069 | | 1970 | 9.5544610176773 | | 1969 | 9.6318912535243 | | 1968 | 9.630209696098 | | 1967 | 9.3614490772447 | | 1966 | 9.423817692257 | | 1965 | 9.4964786827746 | | 1964 | 9.3688294101797 | | 1963 | 9.6576936236089 | | 1962 | 9.7052012863574 | | 1961 | 9.4879402132828 | | 1960 | 9.6469616743577 |
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