| Year | Value | | 2022 | 50.449937383077 | | 2021 | 50.463537925583 | | 2020 | 50.475820462943 | | 2019 | 50.487786129522 | | 2018 | 50.500825930757 | | 2017 | 50.514237909676 | | 2016 | 50.527142169118 | | 2015 | 50.538080704721 | | 2014 | 50.541986936171 | | 2013 | 50.540010661338 | | 2012 | 50.542983459205 | | 2011 | 50.545270006663 | | 2010 | 50.542484438917 | | 2009 | 50.54189140312 | | 2008 | 50.542894093451 | | 2007 | 50.545322711775 | | 2006 | 50.544859490321 | | 2005 | 50.541974828937 | | 2004 | 50.539281324637 | | 2003 | 50.5336572826 | | 2002 | 50.532737922565 | | 2001 | 50.541011696235 | | 2000 | 50.551791224698 | | 1999 | 50.559428107752 | | 1998 | 50.563363557275 | | 1997 | 50.558466160921 | | 1996 | 50.544514923472 | | 1995 | 50.537181083006 | | 1994 | 50.536044720445 | | 1993 | 50.532144335996 | | 1992 | 50.526699868996 | | 1991 | 50.523855817755 | | 1990 | 50.523218208972 | | 1989 | 50.52757729839 | | 1988 | 50.537960196174 | | 1987 | 50.555724172816 | | 1986 | 50.578299553686 | | 1985 | 50.599198160266 | | 1984 | 50.614804799014 | | 1983 | 50.632584129937 | | 1982 | 50.657342812189 | | 1981 | 50.633973813976 | | 1980 | 50.595509024857 | | 1979 | 50.59632766832 | | 1978 | 50.592351052189 | | 1977 | 50.586832781354 | | 1976 | 50.591249619844 | | 1975 | 50.600511619663 | | 1974 | 50.607154589023 | | 1973 | 50.620580509004 | | 1972 | 50.634695589846 | | 1971 | 50.642875962063 | | 1970 | 50.647579070101 | | 1969 | 50.650877630019 | | 1968 | 50.65226030352 | | 1967 | 50.651730844171 | | 1966 | 50.650636752632 | | 1965 | 50.634404607963 | | 1964 | 50.603318842046 | | 1963 | 50.575790462517 | | 1962 | 50.55257053455 | | 1961 | 50.530528998186 | | 1960 | 50.51826588067 |
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