| Year | Value | | 2021 | 35.99234078118 | | 2020 | 36.361134711501 | | 2019 | 36.764661619397 | | 2018 | 37.190469090815 | | 2017 | 37.657038304212 | | 2016 | 38.13540811771 | | 2015 | 38.634099138132 | | 2014 | 39.145494647007 | | 2013 | 39.654677106569 | | 2012 | 40.180139692109 | | 2011 | 40.707699507543 | | 2010 | 41.111289226932 | | 2009 | 41.440499527545 | | 2008 | 41.692537076819 | | 2007 | 41.9742406222 | | 2006 | 42.228403886877 | | 2005 | 42.417535394422 | | 2004 | 42.645027569148 | | 2003 | 42.915114325482 | | 2002 | 43.176037154352 | | 2001 | 43.423999391676 | | 2000 | 43.624639232321 | | 1999 | 43.791513682681 | | 1998 | 43.855203692959 | | 1997 | 44.156336636427 | | 1996 | 44.496573028753 | | 1995 | 44.74794221623 | | 1994 | 44.773250625001 | | 1993 | 45.028831043171 | | 1992 | 45.187244198861 | | 1991 | 45.369326501176 | | 1990 | 45.560077419547 | | 1989 | 45.824768588237 | | 1988 | 45.941875456296 | | 1987 | 46.179916593807 | | 1986 | 46.421014286248 | | 1985 | 46.710061287558 | | 1984 | 46.953696448746 | | 1983 | 47.200015677467 | | 1982 | 47.311377581569 | | 1981 | 47.544137565424 | | 1980 | 47.743777038691 | | 1979 | 47.931721138868 | | 1978 | 48.018507649507 | | 1977 | 48.042041250704 | | 1976 | 48.074829684405 | | 1975 | 48.179972060902 | | 1974 | 48.192393406423 | | 1973 | 48.192871559896 | | 1972 | 48.313833324871 | | 1971 | 48.400355085228 | | 1970 | 48.363104081379 | | 1969 | 48.403459853739 | | 1968 | 48.422166808386 | | 1967 | 48.429884231537 | | 1966 | 48.440994494153 | | 1965 | 48.424306839791 | | 1964 | 48.415148448328 | | 1963 | 48.400766061605 | | 1962 | 48.368197474839 | | 1961 | 47.967274282996 | | 1960 | 47.731154378191 |
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