| Year | Value | | 2022 | 50.497095907327 | | 2021 | 50.545087001498 | | 2020 | 50.601058078087 | | 2019 | 50.659454831311 | | 2018 | 50.718138817276 | | 2017 | 50.77687335882 | | 2016 | 50.83597381622 | | 2015 | 50.895575127341 | | 2014 | 50.950785061178 | | 2013 | 50.998181372323 | | 2012 | 51.040294088221 | | 2011 | 51.076512150745 | | 2010 | 51.106354562739 | | 2009 | 51.129212612619 | | 2008 | 51.146556708972 | | 2007 | 51.162038594534 | | 2006 | 51.177641997707 | | 2005 | 51.194308182131 | | 2004 | 51.21225875227 | | 2003 | 51.231124830526 | | 2002 | 51.253000889104 | | 2001 | 51.279063130701 | | 2000 | 51.307406721573 | | 1999 | 51.337512235774 | | 1998 | 51.368146195501 | | 1997 | 51.398743955338 | | 1996 | 51.430930108218 | | 1995 | 51.464660037624 | | 1994 | 51.497833656975 | | 1993 | 51.528123089235 | | 1992 | 51.562260450576 | | 1991 | 51.603696122485 | | 1990 | 51.647020943701 | | 1989 | 51.691866758494 | | 1988 | 51.739020304727 | | 1987 | 51.788667674208 | | 1986 | 51.840709226179 | | 1985 | 51.895194154745 | | 1984 | 51.951556810725 | | 1983 | 52.009537080499 | | 1982 | 52.069482756188 | | 1981 | 52.131744962299 | | 1980 | 52.195769918742 | | 1979 | 52.261369775066 | | 1978 | 52.328587517901 | | 1977 | 52.397656393225 | | 1976 | 52.470187794671 | | 1975 | 52.549007812595 | | 1974 | 52.635511025672 | | 1973 | 52.73111773336 | | 1972 | 52.844287006838 | | 1971 | 52.971090312559 | | 1970 | 53.104182543581 | | 1969 | 53.24684616686 | | 1968 | 53.397081731153 | | 1967 | 53.557651032539 | | 1966 | 53.721855203135 | | 1965 | 53.880894976982 | | 1964 | 54.040285988146 | | 1963 | 54.205820234583 | | 1962 | 54.372737419344 | | 1961 | 54.534215750159 | | 1960 | 54.703386318723 |
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