| Year | Value | | 2022 | 50.439259828923 | | 2021 | 50.448087506212 | | 2020 | 50.459804950103 | | 2019 | 50.467124412712 | | 2018 | 50.474515808954 | | 2017 | 50.493393133989 | | 2016 | 50.509925382566 | | 2015 | 50.532389149892 | | 2014 | 50.524548334147 | | 2013 | 50.483696069065 | | 2012 | 50.459037583113 | | 2011 | 50.407844557631 | | 2010 | 50.334052736328 | | 2009 | 50.238055447896 | | 2008 | 50.107717379781 | | 2007 | 49.993417180562 | | 2006 | 49.987508282552 | | 2005 | 50.10438666646 | | 2004 | 50.237477907734 | | 2003 | 50.317667014845 | | 2002 | 50.328226840646 | | 2001 | 50.307702914951 | | 2000 | 50.31414584964 | | 1999 | 50.340814513892 | | 1998 | 50.358050891804 | | 1997 | 50.368995783141 | | 1996 | 50.368755281796 | | 1995 | 50.358571435755 | | 1994 | 50.323200721021 | | 1993 | 50.288715909411 | | 1992 | 50.282524465284 | | 1991 | 50.292641102715 | | 1990 | 50.313940483862 | | 1989 | 50.316164434214 | | 1988 | 50.251055594149 | | 1987 | 50.147422944474 | | 1986 | 50.069360909687 | | 1985 | 50.01165222238 | | 1984 | 49.96463694069 | | 1983 | 49.922240845771 | | 1982 | 49.874044248803 | | 1981 | 49.826049607761 | | 1980 | 49.79652867691 | | 1979 | 49.775172156193 | | 1978 | 49.757727182384 | | 1977 | 49.760435953104 | | 1976 | 49.773111028829 | | 1975 | 49.785095817847 | | 1974 | 49.795231598737 | | 1973 | 49.801846687631 | | 1972 | 49.809289853543 | | 1971 | 49.817791288939 | | 1970 | 49.815651150908 | | 1969 | 49.804160450626 | | 1968 | 49.796785328401 | | 1967 | 49.795802264855 | | 1966 | 49.79408811222 | | 1965 | 49.787389641218 | | 1964 | 49.779272554517 | | 1963 | 49.77622872367 | | 1962 | 49.772650278148 | | 1961 | 49.759049235751 | | 1960 | 49.720550950938 |
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