| Year | Value | | 2022 | 50.725477203934 | | 2021 | 50.724614409959 | | 2020 | 50.719379149617 | | 2019 | 50.714729039527 | | 2018 | 50.715959096398 | | 2017 | 50.719092197986 | | 2016 | 50.722566942678 | | 2015 | 50.725336019222 | | 2014 | 50.727175971173 | | 2013 | 50.728464440591 | | 2012 | 50.729437351829 | | 2011 | 50.730199629688 | | 2010 | 50.730702589974 | | 2009 | 50.730932917481 | | 2008 | 50.730922488776 | | 2007 | 50.730893330715 | | 2006 | 50.730739260347 | | 2005 | 50.730345585936 | | 2004 | 50.720495605176 | | 2003 | 50.701137803768 | | 2002 | 50.682125101207 | | 2001 | 50.663923875608 | | 2000 | 50.64685855893 | | 1999 | 50.63128257752 | | 1998 | 50.620256859311 | | 1997 | 50.610258004453 | | 1996 | 50.598195366919 | | 1995 | 50.595424031153 | | 1994 | 50.600874329227 | | 1993 | 50.605751797837 | | 1992 | 50.610976939681 | | 1991 | 50.616818058604 | | 1990 | 50.620958318945 | | 1989 | 50.623194824876 | | 1988 | 50.61281221712 | | 1987 | 50.569217572257 | | 1986 | 50.510784350121 | | 1985 | 50.450487558709 | | 1984 | 50.382378450843 | | 1983 | 50.324079885957 | | 1982 | 50.296514281885 | | 1981 | 50.289743614648 | | 1980 | 50.283670101707 | | 1979 | 50.218849389496 | | 1978 | 50.126001104667 | | 1977 | 50.088953098056 | | 1976 | 50.078712000255 | | 1975 | 50.074209236802 | | 1974 | 50.071013006954 | | 1973 | 50.067971374118 | | 1972 | 50.073640644411 | | 1971 | 50.079252229575 | | 1970 | 50.07479240353 | | 1969 | 50.070078402457 | | 1968 | 50.066381530136 | | 1967 | 50.064736338559 | | 1966 | 50.066395256193 | | 1965 | 50.072621379907 | | 1964 | 50.083500705859 | | 1963 | 50.098487109438 | | 1962 | 50.116148141603 | | 1961 | 50.135094842868 | | 1960 | 50.154720051138 |
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