| Year | Value | | 2022 | 50.545155317836 | | 2021 | 50.493456757825 | | 2020 | 50.442152011024 | | 2019 | 50.397294255332 | | 2018 | 50.353593272171 | | 2017 | 50.310730795934 | | 2016 | 50.27010481087 | | 2015 | 50.233739316604 | | 2014 | 50.200224251161 | | 2013 | 50.169561668717 | | 2012 | 50.146715648899 | | 2011 | 50.135060559412 | | 2010 | 50.138941702987 | | 2009 | 50.171491207392 | | 2008 | 50.22719722855 | | 2007 | 50.283551618333 | | 2006 | 50.330389860035 | | 2005 | 50.371857351892 | | 2004 | 50.418597288098 | | 2003 | 50.467043245199 | | 2002 | 50.518853639392 | | 2001 | 50.561042131088 | | 2000 | 50.576175548589 | | 1999 | 50.581336568598 | | 1998 | 50.597685760734 | | 1997 | 50.618832580699 | | 1996 | 50.638115464801 | | 1995 | 50.656391944758 | | 1994 | 50.675141636945 | | 1993 | 50.693495743464 | | 1992 | 50.70891954651 | | 1991 | 50.731277899465 | | 1990 | 50.764225128425 | | 1989 | 50.798465010644 | | 1988 | 50.832972739074 | | 1987 | 50.867085831262 | | 1986 | 50.902010236629 | | 1985 | 50.938222687588 | | 1984 | 50.973397129187 | | 1983 | 51.019152911865 | | 1982 | 51.07295117042 | | 1981 | 51.129457908626 | | 1980 | 51.201565364662 | | 1979 | 51.285335208391 | | 1978 | 51.369285416152 | | 1977 | 51.449495168349 | | 1976 | 51.531021592121 | | 1975 | 51.618429195404 | | 1974 | 51.714962638965 | | 1973 | 51.810126348114 | | 1972 | 51.903585485219 | | 1971 | 52.000839846919 | | 1970 | 52.103986807644 | | 1969 | 52.155897839673 | | 1968 | 52.147410358566 | | 1967 | 52.133350796417 | | 1966 | 52.117685424862 | | 1965 | 52.10051121372 | | 1964 | 52.084462417143 | | 1963 | 52.065087946716 | | 1962 | 52.04587361308 | | 1961 | 52.025096754024 | | 1960 | 52.013884340821 |
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