| Year | Value | | 2022 | 49.416379484932 | | 2021 | 49.402603607236 | | 2020 | 49.392540716916 | | 2019 | 49.375146931297 | | 2018 | 49.350148953849 | | 2017 | 49.321917310161 | | 2016 | 49.291468948775 | | 2015 | 49.257791153012 | | 2014 | 49.22330278751 | | 2013 | 49.188833798581 | | 2012 | 49.151240707247 | | 2011 | 49.114749240919 | | 2010 | 49.080203726451 | | 2009 | 49.045514528469 | | 2008 | 49.008452912501 | | 2007 | 48.969278432383 | | 2006 | 48.932574826861 | | 2005 | 48.896072868357 | | 2004 | 48.859058603902 | | 2003 | 48.821701813279 | | 2002 | 48.785447528283 | | 2001 | 48.753472888791 | | 2000 | 48.724752843426 | | 1999 | 48.696948293962 | | 1998 | 48.671523262963 | | 1997 | 48.649554804947 | | 1996 | 48.63090330746 | | 1995 | 48.617120721009 | | 1994 | 48.607179259992 | | 1993 | 48.598837732027 | | 1992 | 48.593191285435 | | 1991 | 48.590462524277 | | 1990 | 48.590294058557 | | 1989 | 48.590840099286 | | 1988 | 48.592548321897 | | 1987 | 48.597933190186 | | 1986 | 48.605194158751 | | 1985 | 48.612935621664 | | 1984 | 48.621869231139 | | 1983 | 48.631732843304 | | 1982 | 48.639400017003 | | 1981 | 48.644827493145 | | 1980 | 48.64876332787 | | 1979 | 48.649050174109 | | 1978 | 48.645976882819 | | 1977 | 48.640581073748 | | 1976 | 48.631123786134 | | 1975 | 48.619513780425 | | 1974 | 48.605871673992 | | 1973 | 48.588382461259 | | 1972 | 48.569263440463 | | 1971 | 48.549146489856 | | 1970 | 48.528875906677 | | 1969 | 48.511700152068 | | 1968 | 48.494073980785 | | 1967 | 48.474431569948 | | 1966 | 48.455074698543 | | 1965 | 48.435324900725 | | 1964 | 48.413402894461 | | 1963 | 48.38901711978 | | 1962 | 48.362569459813 | | 1961 | 48.332581080989 | | 1960 | 48.300635268051 |
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