| Year | Value | | 2022 | 49.232612538099 | | 2021 | 49.21620312389 | | 2020 | 49.202522694495 | | 2019 | 49.188935961279 | | 2018 | 49.180426520497 | | 2017 | 49.167228947873 | | 2016 | 49.132677699858 | | 2015 | 49.018764533688 | | 2014 | 48.885346778272 | | 2013 | 48.816073609662 | | 2012 | 48.765385745555 | | 2011 | 48.721601201259 | | 2010 | 48.695734421928 | | 2009 | 48.680865906303 | | 2008 | 48.665103337515 | | 2007 | 48.655735538816 | | 2006 | 48.643919764028 | | 2005 | 48.610763004018 | | 2004 | 48.565079106331 | | 2003 | 48.528898152043 | | 2002 | 48.486531488087 | | 2001 | 48.423197795519 | | 2000 | 48.365330791313 | | 1999 | 48.324725513513 | | 1998 | 48.293438376943 | | 1997 | 48.271069510548 | | 1996 | 48.254664684437 | | 1995 | 48.238683949862 | | 1994 | 48.20988070492 | | 1993 | 48.154347007151 | | 1992 | 48.078044428029 | | 1991 | 47.983144649093 | | 1990 | 47.866906098652 | | 1989 | 47.754997741946 | | 1988 | 47.668247984081 | | 1987 | 47.59819237809 | | 1986 | 47.533489057052 | | 1985 | 47.47053535559 | | 1984 | 47.42003208811 | | 1983 | 47.380260374568 | | 1982 | 47.34979737268 | | 1981 | 47.301804471291 | | 1980 | 47.248667483443 | | 1979 | 47.233666437849 | | 1978 | 47.238206043214 | | 1977 | 47.233966460482 | | 1976 | 47.222341581839 | | 1975 | 47.243657916152 | | 1974 | 47.295061359505 | | 1973 | 47.288872937226 | | 1972 | 47.223702436345 | | 1971 | 47.162161279108 | | 1970 | 47.112621446878 | | 1969 | 47.070594048599 | | 1968 | 47.035868746534 | | 1967 | 46.983335660818 | | 1966 | 46.89854940224 | | 1965 | 46.813843624551 | | 1964 | 46.745323900372 | | 1963 | 46.692998393838 | | 1962 | 46.646028800526 | | 1961 | 46.607893516771 | | 1960 | 46.579355892165 |
|