| Year | Value | | 2022 | 50.280620889523 | | 2021 | 50.275120125866 | | 2020 | 50.270321296169 | | 2019 | 50.267057172071 | | 2018 | 50.26523016376 | | 2017 | 50.264446308903 | | 2016 | 50.261822297517 | | 2015 | 50.254633570339 | | 2014 | 50.244288340817 | | 2013 | 50.232062821795 | | 2012 | 50.225900229272 | | 2011 | 50.217526885186 | | 2010 | 50.194162835852 | | 2009 | 50.236600095416 | | 2008 | 50.352512854276 | | 2007 | 50.469654252843 | | 2006 | 50.590718483656 | | 2005 | 50.718609167111 | | 2004 | 50.8501119028 | | 2003 | 50.986587903493 | | 2002 | 51.130843076637 | | 2001 | 51.282948248555 | | 2000 | 51.441677159461 | | 1999 | 51.545392069426 | | 1998 | 51.591271517943 | | 1997 | 51.638206077268 | | 1996 | 51.688689261699 | | 1995 | 51.745093368208 | | 1994 | 51.80789483512 | | 1993 | 51.877350037907 | | 1992 | 51.952496026936 | | 1991 | 52.027387777989 | | 1990 | 52.099088497736 | | 1989 | 52.180650565406 | | 1988 | 52.273711686054 | | 1987 | 52.372404062882 | | 1986 | 52.478134957635 | | 1985 | 52.589194819256 | | 1984 | 52.70439051727 | | 1983 | 52.826078417747 | | 1982 | 52.957688642096 | | 1981 | 53.096687539253 | | 1980 | 53.095191562065 | | 1979 | 52.904982563417 | | 1978 | 52.670805460641 | | 1977 | 52.432374777384 | | 1976 | 52.189632428383 | | 1975 | 51.94250513347 | | 1974 | 51.698477204474 | | 1973 | 51.458432907407 | | 1972 | 51.216570423627 | | 1971 | 51.029454353418 | | 1970 | 51.008487025781 | | 1969 | 51.149990665077 | | 1968 | 51.346285188265 | | 1967 | 51.549983118996 | | 1966 | 51.759845859863 | | 1965 | 51.972099805043 | | 1964 | 52.181822797235 | | 1963 | 52.39408427806 | | 1962 | 52.608766321721 | | 1961 | 52.787865243868 | | 1960 | 52.885169812579 |
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