| Year | Value | | 2022 | 49.882952623954 | | 2021 | 49.844272994714 | | 2020 | 49.797296651972 | | 2019 | 49.764475179614 | | 2018 | 49.747844063512 | | 2017 | 49.730948264501 | | 2016 | 49.71401529697 | | 2015 | 49.697337757105 | | 2014 | 49.680529985059 | | 2013 | 49.663005455748 | | 2012 | 49.645093894366 | | 2011 | 49.627865673821 | | 2010 | 49.611298537552 | | 2009 | 49.59517245352 | | 2008 | 49.579898696364 | | 2007 | 49.565684895057 | | 2006 | 49.552059000721 | | 2005 | 49.538346925604 | | 2004 | 49.524867899507 | | 2003 | 49.510366024251 | | 2002 | 49.495375752352 | | 2001 | 49.482316886049 | | 2000 | 49.493544254536 | | 1999 | 49.530859627361 | | 1998 | 49.574788148274 | | 1997 | 49.626911753917 | | 1996 | 49.685701007351 | | 1995 | 49.751060738476 | | 1994 | 49.823635426391 | | 1993 | 49.903313531241 | | 1992 | 49.954039661534 | | 1991 | 49.970468844873 | | 1990 | 49.986697094245 | | 1989 | 50.00373427557 | | 1988 | 50.022148501662 | | 1987 | 50.042543392309 | | 1986 | 50.064926572179 | | 1985 | 50.088761797974 | | 1984 | 50.113724954518 | | 1983 | 50.139413980937 | | 1982 | 50.165762049754 | | 1981 | 50.193740736382 | | 1980 | 50.222660461276 | | 1979 | 50.252015015026 | | 1978 | 50.281436903086 | | 1977 | 50.309615156237 | | 1976 | 50.336371202941 | | 1975 | 50.36204779616 | | 1974 | 50.388620128785 | | 1973 | 50.415748040491 | | 1972 | 50.441027626495 | | 1971 | 50.465641142025 | | 1970 | 50.490274861401 | | 1969 | 50.514277664019 | | 1968 | 50.536253468418 | | 1967 | 50.557136235239 | | 1966 | 50.577405439735 | | 1965 | 50.596608780781 | | 1964 | 50.615217080551 | | 1963 | 50.631252171652 | | 1962 | 50.646094603198 | | 1961 | 50.661075095172 | | 1960 | 50.673375562877 |
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