| Year | Value | | 2022 | 50.747991638861 | | 2021 | 50.725748468615 | | 2020 | 50.697397974382 | | 2019 | 50.676888809872 | | 2018 | 50.665195499364 | | 2017 | 50.655594031151 | | 2016 | 50.645878150489 | | 2015 | 50.636491537538 | | 2014 | 50.628062621816 | | 2013 | 50.619261383474 | | 2012 | 50.608938877826 | | 2011 | 50.598590448889 | | 2010 | 50.587551607547 | | 2009 | 50.574275047474 | | 2008 | 50.559411219075 | | 2007 | 50.546926148954 | | 2006 | 50.537373534817 | | 2005 | 50.527729886449 | | 2004 | 50.517579472838 | | 2003 | 50.506939481111 | | 2002 | 50.495695803271 | | 2001 | 50.484503995677 | | 2000 | 50.472211862852 | | 1999 | 50.459973339818 | | 1998 | 50.45011982424 | | 1997 | 50.440288517399 | | 1996 | 50.430197866935 | | 1995 | 50.420235766914 | | 1994 | 50.411246193605 | | 1993 | 50.400746478922 | | 1992 | 50.387380153623 | | 1991 | 50.373156850898 | | 1990 | 50.359102082948 | | 1989 | 50.345864731774 | | 1988 | 50.333329447492 | | 1987 | 50.321097496977 | | 1986 | 50.308535335936 | | 1985 | 50.296133439069 | | 1984 | 50.282810822944 | | 1983 | 50.268196088119 | | 1982 | 50.252118693808 | | 1981 | 50.235071985201 | | 1980 | 50.218977220657 | | 1979 | 50.202467172066 | | 1978 | 50.18525869232 | | 1977 | 50.168858632445 | | 1976 | 50.149434280121 | | 1975 | 50.127176713718 | | 1974 | 50.104891539358 | | 1973 | 50.081612993314 | | 1972 | 50.057962903661 | | 1971 | 50.033081053602 | | 1970 | 50.015486289969 | | 1969 | 50.005807074609 | | 1968 | 49.995417597211 | | 1967 | 49.985069062568 | | 1966 | 49.974802607235 | | 1965 | 49.963851084812 | | 1964 | 49.952286305405 | | 1963 | 49.940497562324 | | 1962 | 49.92790215174 | | 1961 | 49.913927037156 | | 1960 | 49.898935134548 |
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