| Year | Value | | 2022 | 48.405705673064 | | 2021 | 48.385756416724 | | 2020 | 48.366936785718 | | 2019 | 48.353782544227 | | 2018 | 48.345688655335 | | 2017 | 48.339231963877 | | 2016 | 48.333733491801 | | 2015 | 48.328632525169 | | 2014 | 48.322726253308 | | 2013 | 48.314901153531 | | 2012 | 48.305528039369 | | 2011 | 48.295687552549 | | 2010 | 48.286394840644 | | 2009 | 48.277898790115 | | 2008 | 48.27015696438 | | 2007 | 48.263384319897 | | 2006 | 48.257850933801 | | 2005 | 48.254145710425 | | 2004 | 48.252337193546 | | 2003 | 48.25233441914 | | 2002 | 48.253835398562 | | 2001 | 48.257054070875 | | 2000 | 48.262914539782 | | 1999 | 48.27060710561 | | 1998 | 48.279857916226 | | 1997 | 48.290392027825 | | 1996 | 48.300735161607 | | 1995 | 48.310354438875 | | 1994 | 48.317458365335 | | 1993 | 48.320256197579 | | 1992 | 48.318696803108 | | 1991 | 48.313431234521 | | 1990 | 48.304562031849 | | 1989 | 48.292870639026 | | 1988 | 48.281271636772 | | 1987 | 48.271155728349 | | 1986 | 48.261367372533 | | 1985 | 48.25113509258 | | 1984 | 48.241184533095 | | 1983 | 48.231627035705 | | 1982 | 48.222938890861 | | 1981 | 48.216335443864 | | 1980 | 48.211735519356 | | 1979 | 48.20885629904 | | 1978 | 48.208568729185 | | 1977 | 48.211789473436 | | 1976 | 48.219180921839 | | 1975 | 48.229605015551 | | 1974 | 48.241315327025 | | 1973 | 48.253382519609 | | 1972 | 48.265317297711 | | 1971 | 48.277304006919 | | 1970 | 48.288478702582 | | 1969 | 48.298804064816 | | 1968 | 48.308963646942 | | 1967 | 48.318455758528 | | 1966 | 48.327705877598 | | 1965 | 48.337117487928 | | 1964 | 48.347178889912 | | 1963 | 48.358248888953 | | 1962 | 48.369728032483 | | 1961 | 48.381810311655 | | 1960 | 48.394838883356 |
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