| Year | Value | | 2022 | 52.830626671262 | | 2021 | 52.764994649923 | | 2020 | 52.68804156055 | | 2019 | 52.602199832548 | | 2018 | 52.514845889261 | | 2017 | 52.435533660804 | | 2016 | 52.367205206337 | | 2015 | 52.305827151245 | | 2014 | 52.25339254665 | | 2013 | 52.208564383358 | | 2012 | 52.168569169718 | | 2011 | 52.131506706822 | | 2010 | 52.096063338607 | | 2009 | 52.064208589656 | | 2008 | 52.035690686044 | | 2007 | 52.008136799949 | | 2006 | 51.982152987729 | | 2005 | 51.957202608079 | | 2004 | 51.933738132483 | | 2003 | 51.912130505109 | | 2002 | 51.891746130611 | | 2001 | 51.872313342107 | | 2000 | 51.853906396161 | | 1999 | 51.834550925628 | | 1998 | 51.812514827337 | | 1997 | 51.787330184348 | | 1996 | 51.758473707884 | | 1995 | 51.725922125202 | | 1994 | 51.689574016071 | | 1993 | 51.653695990993 | | 1992 | 51.623346875641 | | 1991 | 51.596445388366 | | 1990 | 51.569455857255 | | 1989 | 51.541593204951 | | 1988 | 51.513000398513 | | 1987 | 51.484735822138 | | 1986 | 51.458858142156 | | 1985 | 51.436596943468 | | 1984 | 51.418884338678 | | 1983 | 51.404556712756 | | 1982 | 51.391927044283 | | 1981 | 51.37880835541 | | 1980 | 51.363106955585 | | 1979 | 51.338920247817 | | 1978 | 51.304308492738 | | 1977 | 51.270826069531 | | 1976 | 51.241103992245 | | 1975 | 51.211314461319 | | 1974 | 51.179506749858 | | 1973 | 51.145052232069 | | 1972 | 51.110850337058 | | 1971 | 51.077922572751 | | 1970 | 51.047351731559 | | 1969 | 51.02694499963 | | 1968 | 51.003173157648 | | 1967 | 50.957754288343 | | 1966 | 50.895645350967 | | 1965 | 50.82432817137 | | 1964 | 50.750767869012 | | 1963 | 50.680194284928 | | 1962 | 50.616831766948 | | 1961 | 50.563612443604 | | 1960 | 50.510555281192 |
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