| Year | Value | | 2022 | 48.903356677113 | | 2021 | 48.897446638546 | | 2020 | 48.892636044339 | | 2019 | 48.885790020015 | | 2018 | 48.875109931511 | | 2017 | 48.859505649799 | | 2016 | 48.84178319423 | | 2015 | 48.820675088819 | | 2014 | 48.802342434869 | | 2013 | 48.791764602454 | | 2012 | 48.78151779018 | | 2011 | 48.772008093018 | | 2010 | 48.766203640768 | | 2009 | 48.760472295764 | | 2008 | 48.751105710476 | | 2007 | 48.735638961138 | | 2006 | 48.719239008666 | | 2005 | 48.701906899023 | | 2004 | 48.681186955966 | | 2003 | 48.662264059165 | | 2002 | 48.646982020707 | | 2001 | 48.638963488427 | | 2000 | 48.637372015239 | | 1999 | 48.636281624547 | | 1998 | 48.634753856839 | | 1997 | 48.631255155091 | | 1996 | 48.625399146874 | | 1995 | 48.617108718113 | | 1994 | 48.605293003693 | | 1993 | 48.589004451967 | | 1992 | 48.569718465497 | | 1991 | 48.549071951174 | | 1990 | 48.527645105595 | | 1989 | 48.507695918571 | | 1988 | 48.489938192712 | | 1987 | 48.47351599053 | | 1986 | 48.457490600435 | | 1985 | 48.443821963557 | | 1984 | 48.433580340355 | | 1983 | 48.424211411038 | | 1982 | 48.415194064615 | | 1981 | 48.406995218588 | | 1980 | 48.387865323573 | | 1979 | 48.370687295781 | | 1978 | 48.36632279688 | | 1977 | 48.360342272951 | | 1976 | 48.352743363702 | | 1975 | 48.344653833266 | | 1974 | 48.332233605648 | | 1973 | 48.316940600354 | | 1972 | 48.301728941456 | | 1971 | 48.28226096141 | | 1970 | 48.260415412277 | | 1969 | 48.241508543742 | | 1968 | 48.221845509376 | | 1967 | 48.196626180321 | | 1966 | 48.167897334571 | | 1965 | 48.137100446013 | | 1964 | 48.104339330711 | | 1963 | 48.070710801142 | | 1962 | 48.036524907446 | | 1961 | 48.003529609145 | | 1960 | 47.971896712325 |
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