| Year | Value | | 2022 | 47.930910568847 | | 2021 | 47.926828984171 | | 2020 | 47.938279465698 | | 2019 | 47.952116562826 | | 2018 | 47.956810349675 | | 2017 | 47.958627600176 | | 2016 | 47.964938755857 | | 2015 | 47.97622074671 | | 2014 | 47.989636742507 | | 2013 | 48.007354880796 | | 2012 | 48.027544507894 | | 2011 | 48.048135408359 | | 2010 | 48.071533058052 | | 2009 | 48.098031304232 | | 2008 | 48.123593611328 | | 2007 | 48.149345451649 | | 2006 | 48.176423437598 | | 2005 | 48.197267149401 | | 2004 | 48.209710945463 | | 2003 | 48.214463890354 | | 2002 | 48.225990284491 | | 2001 | 48.248520768351 | | 2000 | 48.274169876278 | | 1999 | 48.308727014336 | | 1998 | 48.346278870744 | | 1997 | 48.375066036055 | | 1996 | 48.395648134734 | | 1995 | 48.41284556068 | | 1994 | 48.428265117314 | | 1993 | 48.442234586068 | | 1992 | 48.454963566447 | | 1991 | 48.477648693144 | | 1990 | 48.49656257899 | | 1989 | 48.500283972791 | | 1988 | 48.501602410163 | | 1987 | 48.502913702618 | | 1986 | 48.504793232099 | | 1985 | 48.507312057061 | | 1984 | 48.509374038246 | | 1983 | 48.510641760103 | | 1982 | 48.513466296004 | | 1981 | 48.516230763531 | | 1980 | 48.51115017211 | | 1979 | 48.493321100105 | | 1978 | 48.467439669589 | | 1977 | 48.438195813983 | | 1976 | 48.405131848584 | | 1975 | 48.370785818346 | | 1974 | 48.338304829981 | | 1973 | 48.305232336424 | | 1972 | 48.274105817051 | | 1971 | 48.25025615083 | | 1970 | 48.228916166785 | | 1969 | 48.203751391339 | | 1968 | 48.174060995058 | | 1967 | 48.138920490204 | | 1966 | 48.097718192021 | | 1965 | 48.04999689265 | | 1964 | 47.997121639952 | | 1963 | 47.938999314397 | | 1962 | 47.875963434307 | | 1961 | 47.77300116787 | | 1960 | 47.712177026436 |
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