| Year | Value | | 2022 | 50.459136308716 | | 2021 | 50.460409454332 | | 2020 | 50.464975414523 | | 2019 | 50.470559007018 | | 2018 | 50.477257790764 | | 2017 | 50.488080272328 | | 2016 | 50.503317593529 | | 2015 | 50.5198969692 | | 2014 | 50.536097212295 | | 2013 | 50.555700936765 | | 2012 | 50.579187430226 | | 2011 | 50.602380871103 | | 2010 | 50.623598843577 | | 2009 | 50.643578010781 | | 2008 | 50.661802954971 | | 2007 | 50.676651089555 | | 2006 | 50.68801575445 | | 2005 | 50.699510313103 | | 2004 | 50.710383352643 | | 2003 | 50.720279185407 | | 2002 | 50.732479982839 | | 2001 | 50.746392629793 | | 2000 | 50.760385123476 | | 1999 | 50.774714240741 | | 1998 | 50.791433272173 | | 1997 | 50.810624629899 | | 1996 | 50.831590946766 | | 1995 | 50.857031724855 | | 1994 | 50.889987193437 | | 1993 | 50.930749277352 | | 1992 | 50.97763353368 | | 1991 | 51.030173882236 | | 1990 | 51.088278886685 | | 1989 | 51.153134658989 | | 1988 | 51.15213425964 | | 1987 | 51.083879584935 | | 1986 | 51.022170222547 | | 1985 | 50.963245718129 | | 1984 | 50.908317560912 | | 1983 | 50.857536267902 | | 1982 | 50.810253721592 | | 1981 | 50.767422655948 | | 1980 | 50.728683437755 | | 1979 | 50.726419199597 | | 1978 | 50.760418687854 | | 1977 | 50.795424929269 | | 1976 | 50.831121638095 | | 1975 | 50.863660838718 | | 1974 | 50.893761499598 | | 1973 | 50.924927391748 | | 1972 | 50.954958267014 | | 1971 | 50.985014356788 | | 1970 | 51.013749232318 | | 1969 | 51.040191964972 | | 1968 | 51.066039764628 | | 1967 | 51.089085164497 | | 1966 | 51.10982719788 | | 1965 | 51.130913317467 | | 1964 | 51.151380714911 | | 1963 | 51.1710004633 | | 1962 | 51.189375071351 | | 1961 | 51.205286002572 | | 1960 | 51.218062834415 |
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