| Year | Value | | 2022 | 49.963525780619 | | 2021 | 49.969595158284 | | 2020 | 49.975675333524 | | 2019 | 49.98055958105 | | 2018 | 49.984934186264 | | 2017 | 49.989648432142 | | 2016 | 49.995501200201 | | 2015 | 50.002871276333 | | 2014 | 50.01334342434 | | 2013 | 50.027051429725 | | 2012 | 50.038982028108 | | 2011 | 50.048059792867 | | 2010 | 50.05587888986 | | 2009 | 50.064973289096 | | 2008 | 50.077945773119 | | 2007 | 50.093480002653 | | 2006 | 50.110038687938 | | 2005 | 50.140049735657 | | 2004 | 50.184970977974 | | 2003 | 50.225217467097 | | 2002 | 50.255814967386 | | 2001 | 50.284283151236 | | 2000 | 50.313332108688 | | 1999 | 50.344282758297 | | 1998 | 50.415507617839 | | 1997 | 50.50561511046 | | 1996 | 50.576902655231 | | 1995 | 50.64965259378 | | 1994 | 50.702418480991 | | 1993 | 50.780672925646 | | 1992 | 50.852520647442 | | 1991 | 50.845422500564 | | 1990 | 50.820676760569 | | 1989 | 50.802682734721 | | 1988 | 50.870876485218 | | 1987 | 50.972534978319 | | 1986 | 50.974886073892 | | 1985 | 50.935180442928 | | 1984 | 50.90319300952 | | 1983 | 50.941029929815 | | 1982 | 50.978526729349 | | 1981 | 50.916369346122 | | 1980 | 50.816105185771 | | 1979 | 50.702978532444 | | 1978 | 50.580694672335 | | 1977 | 50.453876120202 | | 1976 | 50.334419711294 | | 1975 | 50.217132110637 | | 1974 | 50.09165342312 | | 1973 | 50.022923767107 | | 1972 | 50.026034107252 | | 1971 | 50.043324485614 | | 1970 | 50.071851853031 | | 1969 | 50.109842611054 | | 1968 | 50.146871400885 | | 1967 | 50.182568673998 | | 1966 | 50.221024404102 | | 1965 | 50.255503442113 | | 1964 | 50.278333469052 | | 1963 | 50.303973926316 | | 1962 | 50.320618892751 | | 1961 | 50.317738639159 | | 1960 | 50.314119009971 |
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