| Year | Value | | 2022 | 50.117738285014 | | 2021 | 50.049041759058 | | 2020 | 49.988053085461 | | 2019 | 49.939332951272 | | 2018 | 49.906065770297 | | 2017 | 49.878531823967 | | 2016 | 49.856563358733 | | 2015 | 49.84241006272 | | 2014 | 49.837696447629 | | 2013 | 49.840596547159 | | 2012 | 49.852205575492 | | 2011 | 49.876993257383 | | 2010 | 49.917536183681 | | 2009 | 49.973298445577 | | 2008 | 50.04006180868 | | 2007 | 50.114042479984 | | 2006 | 50.188603733052 | | 2005 | 50.260169872131 | | 2004 | 50.327823675269 | | 2003 | 50.385694623748 | | 2002 | 50.425589337264 | | 2001 | 50.439400915522 | | 2000 | 50.421697405517 | | 1999 | 50.37113575583 | | 1998 | 50.293007030869 | | 1997 | 50.186386716247 | | 1996 | 50.058279030768 | | 1995 | 49.917183357265 | | 1994 | 49.76331201072 | | 1993 | 49.601282875114 | | 1992 | 49.43456489753 | | 1991 | 49.269354688755 | | 1990 | 49.108667322597 | | 1989 | 48.954597886406 | | 1988 | 48.812280896924 | | 1987 | 48.684025208205 | | 1986 | 48.568376441477 | | 1985 | 48.463974651018 | | 1984 | 48.371920148825 | | 1983 | 48.294267548514 | | 1982 | 48.230998569963 | | 1981 | 48.182539101701 | | 1980 | 48.149559550062 | | 1979 | 48.130428145196 | | 1978 | 48.121422475589 | | 1977 | 48.122041448107 | | 1976 | 48.131568861569 | | 1975 | 48.148160726185 | | 1974 | 48.17424574117 | | 1973 | 48.209198725935 | | 1972 | 48.249470199835 | | 1971 | 48.293129334023 | | 1970 | 48.340517677099 | | 1969 | 48.390232936646 | | 1968 | 48.440877699768 | | 1967 | 48.491706460618 | | 1966 | 48.542489963486 | | 1965 | 48.592712966386 | | 1964 | 48.642928497655 | | 1963 | 48.691363987328 | | 1962 | 48.734351001405 | | 1961 | 48.769444439734 | | 1960 | 48.797122936157 |
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