| Year | Value | | 2022 | 50.504027871323 | | 2021 | 50.518942611508 | | 2020 | 50.538234925325 | | 2019 | 50.551564656654 | | 2018 | 50.559706377732 | | 2017 | 50.566266045009 | | 2016 | 50.572256584213 | | 2015 | 50.575271395172 | | 2014 | 50.574858821504 | | 2013 | 50.574173989486 | | 2012 | 50.573738366274 | | 2011 | 50.57263456442 | | 2010 | 50.571369016317 | | 2009 | 50.57034378207 | | 2008 | 50.569438873171 | | 2007 | 50.567538254729 | | 2006 | 50.564322736345 | | 2005 | 50.560921962065 | | 2004 | 50.557014271968 | | 2003 | 50.552015840109 | | 2002 | 50.546437523986 | | 2001 | 50.540437251471 | | 2000 | 50.531739031912 | | 1999 | 50.521110210897 | | 1998 | 50.511511604856 | | 1997 | 50.501096621446 | | 1996 | 50.491683802386 | | 1995 | 50.485576131232 | | 1994 | 50.480471924713 | | 1993 | 50.476639172377 | | 1992 | 50.473637481007 | | 1991 | 50.467226607139 | | 1990 | 50.458281255785 | | 1989 | 50.44861315873 | | 1988 | 50.43970080806 | | 1987 | 50.431732885361 | | 1986 | 50.424452787448 | | 1985 | 50.424753725273 | | 1984 | 50.430733307352 | | 1983 | 50.435800419784 | | 1982 | 50.439424735756 | | 1981 | 50.438259073439 | | 1980 | 50.433704367563 | | 1979 | 50.431153689754 | | 1978 | 50.428634604281 | | 1977 | 50.423176351814 | | 1976 | 50.41893835626 | | 1975 | 50.413257530844 | | 1974 | 50.40192439888 | | 1973 | 50.387560991538 | | 1972 | 50.371683105392 | | 1971 | 50.355104184044 | | 1970 | 50.345168581271 | | 1969 | 50.339390041135 | | 1968 | 50.330313307405 | | 1967 | 50.322095882366 | | 1966 | 50.314394375879 | | 1965 | 50.306743196697 | | 1964 | 50.299507902325 | | 1963 | 50.288824675416 | | 1962 | 50.277473236394 | | 1961 | 50.272370241069 | | 1960 | 50.27453571222 |
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