| Year | Value | | 2021 | 57.707528957529 | | 2020 | 57.707528957529 | | 2019 | 57.707528957529 | | 2018 | 57.707528957529 | | 2017 | 58.166023166023 | | 2016 | 58.59555984556 | | 2015 | 59.025096525097 | | 2014 | 58.600386100386 | | 2013 | 58.803088803089 | | 2012 | 58.986486486486 | | 2011 | 59.169884169884 | | 2010 | 59.358108108108 | | 2009 | 59.541505791506 | | 2008 | 59.724903474903 | | 2007 | 59.908301158301 | | 2006 | 58.730694980695 | | 2005 | 58.812741312741 | | 2004 | 61.809845559846 | | 2003 | 60.555019305019 | | 2002 | 60.989382239382 | | 2001 | 61.665057915058 | | 2000 | 62.099420849421 | | 1999 | 62.533783783784 | | 1998 | 61.283783783784 | | 1997 | 59.893822393822 | | 1996 | 60.139961389961 | | 1995 | 62.26833976834 | | 1994 | 62.466216216216 | | 1993 | 62.567567567568 | | 1992 | 62.813706563707 | | 1991 | 61.954633204633 | | 1990 | 61.332046332046 | | 1989 | 60.950772200772 | | 1988 | 61.196911196911 | | 1987 | 60.477799227799 | | 1986 | 60.723938223938 | | 1985 | 60.004826254826 | | 1984 | 59.29054054054 | | 1983 | 59.054054054054 | | 1982 | 59.493243243243 | | 1981 | 61.138996138996 | | 1980 | 63.315637065637 | | 1979 | 63.079150579151 | | 1978 | 60.916988416988 | | 1977 | 59.184362934363 | | 1976 | 58.996138996139 | | 1975 | 59.256594724221 | | 1974 | 59.021582733813 | | 1973 | 58.786570743405 | | 1972 | 58.695443645084 | | 1971 | 58.800959232614 | | 1970 | 56.983213429257 | | 1969 | 57.323741007194 | | 1968 | 57.664268585132 | | 1967 | 58.196642685851 | | 1966 | 58.681055155875 | | 1965 | 59.218225419664 | | 1964 | 59.654676258993 | | 1963 | 60.043165467626 | | 1962 | 60.047961630695 | | 1961 | 60.047961630695 |
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