| Year | Value | | 2024 | 50.431924786219 | | 2023 | 50.422353923828 | | 2022 | 50.412454181529 | | 2021 | 50.400847626174 | | 2020 | 50.386992982189 | | 2019 | 50.374571740868 | | 2018 | 50.36473197168 | | 2017 | 50.354792807636 | | 2016 | 50.344913323542 | | 2015 | 50.334995569983 | | 2014 | 50.325066793522 | | 2013 | 50.316452161552 | | 2012 | 50.309026043008 | | 2011 | 50.302406708295 | | 2010 | 50.29572631932 | | 2009 | 50.28852651811 | | 2008 | 50.280150638376 | | 2007 | 50.270603423336 | | 2006 | 50.261754408926 | | 2005 | 50.253286890452 | | 2004 | 50.245786644362 | | 2003 | 50.242588064938 | | 2002 | 50.245483135447 | | 2001 | 50.254047319311 | | 2000 | 50.266285570534 | | 1999 | 50.279611940051 | | 1998 | 50.293771528827 | | 1997 | 50.309533697421 | | 1996 | 50.324593698764 | | 1995 | 50.337401314854 | | 1994 | 50.347848287086 | | 1993 | 50.357267865428 | | 1992 | 50.347598281178 | | 1991 | 50.332122733294 | | 1990 | 50.333627245103 | | 1989 | 50.342024709852 | | 1988 | 50.351376508442 | | 1987 | 50.361797367066 | | 1986 | 50.372705480577 | | 1985 | 50.382926732358 | | 1984 | 50.391742806331 | | 1983 | 50.399807334807 | | 1982 | 50.408679643915 | | 1981 | 50.418455780112 | | 1980 | 50.427696699047 | | 1979 | 50.435941979489 | | 1978 | 50.444772185937 | | 1977 | 50.453433249677 | | 1976 | 50.461781162102 | | 1975 | 50.471158793376 |
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