| Year | Value | | 2022 | 48.638602379958 | | 2021 | 48.622048491127 | | 2020 | 48.60777390338 | | 2019 | 48.593725760026 | | 2018 | 48.577596013651 | | 2017 | 48.560482657536 | | 2016 | 48.542235544098 | | 2015 | 48.522304403663 | | 2014 | 48.503480344601 | | 2013 | 48.483295397283 | | 2012 | 48.457309364954 | | 2011 | 48.427198457899 | | 2010 | 48.392280096331 | | 2009 | 48.353359537621 | | 2008 | 48.31347565698 | | 2007 | 48.301951552162 | | 2006 | 48.330039844318 | | 2005 | 48.372697333762 | | 2004 | 48.421564726844 | | 2003 | 48.474784630829 | | 2002 | 48.532343083261 | | 2001 | 48.594203334638 | | 2000 | 48.663386523236 | | 1999 | 48.750359487499 | | 1998 | 48.790817311527 | | 1997 | 48.76141930724 | | 1996 | 48.720337115616 | | 1995 | 48.67700549481 | | 1994 | 48.658130703146 | | 1993 | 48.663913552515 | | 1992 | 48.668340019495 | | 1991 | 48.671994258504 | | 1990 | 48.675723937895 | | 1989 | 48.678954909021 | | 1988 | 48.682314269198 | | 1987 | 48.661299497239 | | 1986 | 48.629393415955 | | 1985 | 48.611935510692 | | 1984 | 48.593255595243 | | 1983 | 48.576041569116 | | 1982 | 48.559839288881 | | 1981 | 48.543296199277 | | 1980 | 48.525912547993 | | 1979 | 48.507631270795 | | 1978 | 48.489793950912 | | 1977 | 48.472908089367 | | 1976 | 48.454918938639 | | 1975 | 48.431318897209 | | 1974 | 48.399175801328 | | 1973 | 48.365500529498 | | 1972 | 48.337148256733 | | 1971 | 48.312401950035 | | 1970 | 48.289662952978 | | 1969 | 48.268249343377 | | 1968 | 48.246412455745 | | 1967 | 48.227113140812 | | 1966 | 48.213309076818 | | 1965 | 48.201179869296 | | 1964 | 48.190903028573 | | 1963 | 48.184649380989 | | 1962 | 48.183977752948 | | 1961 | 48.186326871336 | | 1960 | 48.184119604063 |
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