| Year | Value | | 2021 | 62.438851699279 | | 2020 | 62.438851699279 | | 2019 | 62.438851699279 | | 2018 | 62.438851699279 | | 2017 | 62.711766220391 | | 2016 | 62.45236869207 | | 2015 | 63.298146240989 | | 2014 | 62.828269824923 | | 2013 | 63.999742533471 | | 2012 | 63.864572605561 | | 2011 | 64.830072090628 | | 2010 | 64.61122554068 | | 2009 | 63.008496395469 | | 2008 | 63.600669412976 | | 2007 | 63.111483007209 | | 2006 | 63.117919670443 | | 2005 | 63.233779608651 | | 2004 | 63.272399588054 | | 2003 | 62.9763130793 | | 2002 | 62.84114315139 | | 2001 | 61.141864057672 | | 2000 | 61.476570545829 | | 1999 | 61.315653964984 | | 1998 | 60.633367662204 | | 1997 | 60.163491246138 | | 1996 | 60.015447991761 | | 1995 | 60.169927909372 | | 1994 | 59.751544799176 | | 1993 | 60.646240988672 | | 1992 | 60.214984552008 | | 1991 | 59.28166838311 | | 1990 | 59.159371781668 | | 1989 | 59.339598352214 | | 1988 | 59.024201853759 | | 1987 | 59.255921730175 | | 1986 | 59.17868177137 | | 1985 | 59.783728115345 | | 1984 | 60.131307929969 | | 1983 | 59.99613800206 | | 1982 | 59.320288362513 | | 1981 | 58.75386199794 | | 1980 | 58.322605561277 | | 1979 | 59.815911431514 | | 1978 | 60.227857878476 | | 1977 | 60.974510813594 | | 1976 | 60.684860968074 | | 1975 | 60.247167868177 | | 1974 | 59.80947476828 | | 1973 | 59.500514933059 | | 1972 | 58.934088568486 | | 1971 | 58.303295571576 | | 1970 | 58.271112255407 | | 1969 | 57.080329557158 | | 1968 | 56.114830072091 | | 1967 | 56.127703398558 | | 1966 | 56.140576725026 | | 1965 | 56.153450051493 | | 1964 | 56.166323377961 | | 1963 | 55.638516992791 | | 1962 | 55.651390319259 | | 1961 | 55.664263645726 |
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