Year | Value | 2021 | 31.328666964138 | 2020 | 31.632789530028 | 2019 | 31.946229555981 | 2018 | 32.171023832444 | 2017 | 32.424602437207 | 2016 | 32.783148311273 | 2015 | 33.077595734926 | 2014 | 33.382615221757 | 2013 | 33.702524494081 | 2012 | 34.030370826946 | 2011 | 34.443158356258 | 2010 | 34.880050174663 | 2009 | 35.290990039233 | 2008 | 35.673064866786 | 2007 | 36.136482299402 | 2006 | 36.495596583783 | 2005 | 36.840477199974 | 2004 | 37.274741791994 | 2003 | 37.671500005361 | 2002 | 38.075726985428 | 2001 | 38.419686343805 | 2000 | 38.751704915999 | 1999 | 39.117711939832 | 1998 | 39.423491808892 | 1997 | 39.904585303838 | 1996 | 40.237692532764 | 1995 | 40.656173399615 | 1994 | 40.981983767712 | 1993 | 41.346596044397 | 1992 | 41.693361579366 | 1991 | 42.1483093062 | 1990 | 42.658922422323 | 1989 | 43.111145813055 | 1988 | 43.493329515011 | 1987 | 44.02832532755 | 1986 | 44.454638987038 | 1985 | 44.936709906071 | 1984 | 45.283121195686 | 1983 | 45.542761942103 | 1982 | 45.836870898829 | 1981 | 46.002196298648 | 1980 | 46.169686778934 | 1979 | 46.198143124888 | 1978 | 46.073282354903 | 1977 | 46.117088023269 | 1976 | 46.230078742625 | 1975 | 46.32080504539 | 1974 | 46.517811574117 | 1973 | 46.733274997557 | 1972 | 47.051431711665 | 1971 | 47.166673058814 | 1970 | 47.159312021362 | 1969 | 47.189557375278 | 1968 | 47.234232811146 | 1967 | 47.307628696827 | 1966 | 47.33799243759 | 1965 | 47.446294631619 | 1964 | 47.578619407255 | 1963 | 47.688580626241 | 1962 | 47.838061224391 | 1961 | 47.864793991743 | 1960 | 47.85430323274 |
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