| Year | Value | | 2022 | 48.846624439032 | | 2021 | 48.823593076993 | | 2020 | 48.801893144068 | | 2019 | 48.779910152462 | | 2018 | 48.756680294231 | | 2017 | 48.733222759663 | | 2016 | 48.707043700996 | | 2015 | 48.677081480968 | | 2014 | 48.653568131284 | | 2013 | 48.636461279893 | | 2012 | 48.617517675849 | | 2011 | 48.597658793357 | | 2010 | 48.577035327481 | | 2009 | 48.555254464239 | | 2008 | 48.529487449375 | | 2007 | 48.504011169894 | | 2006 | 48.481029530957 | | 2005 | 48.460569967191 | | 2004 | 48.445269390873 | | 2003 | 48.432476023496 | | 2002 | 48.421216548403 | | 2001 | 48.412744795118 | | 2000 | 48.408508459539 | | 1999 | 48.407197152377 | | 1998 | 48.406893420912 | | 1997 | 48.407306916169 | | 1996 | 48.408818121609 | | 1995 | 48.410373963472 | | 1994 | 48.410455137822 | | 1993 | 48.407781648782 | | 1992 | 48.40114865296 | | 1991 | 48.392416373924 | | 1990 | 48.38264062642 | | 1989 | 48.370363840171 | | 1988 | 48.356267647452 | | 1987 | 48.342119928996 | | 1986 | 48.328031203837 | | 1985 | 48.31265659346 | | 1984 | 48.296316341043 | | 1983 | 48.28107016639 | | 1982 | 48.26683256194 | | 1981 | 48.25368488748 | | 1980 | 48.24084028427 | | 1979 | 48.227693073011 | | 1978 | 48.21673004161 | | 1977 | 48.209190860165 | | 1976 | 48.204126490682 | | 1975 | 48.200817096848 | | 1974 | 48.201866949523 | | 1973 | 48.206217124433 | | 1972 | 48.210406428479 | | 1971 | 48.193188344834 | | 1970 | 48.175675848722 | | 1969 | 48.178363797377 | | 1968 | 48.178762159422 | | 1967 | 48.178328562697 | | 1966 | 48.177738185445 | | 1965 | 48.177490516367 | | 1964 | 48.177582603539 | | 1963 | 48.178273117517 | | 1962 | 48.179084108679 | | 1961 | 48.179788821806 | | 1960 | 48.180582323826 |
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