Year | Value | 2021 | 13.550560692457 | 2020 | 13.674069584841 | 2019 | 13.931755751739 | 2018 | 14.1715001017 | 2017 | 14.498449911373 | 2016 | 14.939587829747 | 2015 | 15.368262797176 | 2014 | 15.466229360104 | 2013 | 15.73195795055 | 2012 | 16.136542641722 | 2011 | 16.32027394736 | 2010 | 16.46002547203 | 2009 | 17.07140253495 | 2008 | 17.318267499759 | 2007 | 17.402932977811 | 2006 | 18.020926929628 | 2005 | 18.215527716828 | 2004 | 18.499094905132 | 2003 | 18.667142785042 | 2002 | 18.936605347968 | 2001 | 19.274176059406 | 2000 | 19.591453507301 | 1999 | 20.574796306851 | 1998 | 21.326868179034 | 1997 | 21.847498265969 | 1996 | 22.158238874361 | 1995 | 23.209059459133 | 1994 | 23.751449881055 | 1993 | 24.334649828937 | 1992 | 24.762112871625 | 1991 | 24.827915974901 | 1990 | 25.038475137491 | 1989 | 25.952438075285 | 1988 | 26.564446247733 | 1987 | 27.246526665902 | 1986 | 27.869704781476 | 1985 | 28.367900380009 | 1984 | 28.640250860629 | 1983 | 29.088652146517 | 1982 | 29.27510144427 | 1981 | 29.313707979754 | 1980 | 29.239921942057 | 1979 | 29.292192579037 | 1978 | 29.293711991888 | 1977 | 29.382332256763 | 1976 | 29.424706414036 | 1975 | 29.914666319559 | 1974 | 30.550752285684 | 1973 | 31.238016913771 | 1972 | 31.802420249341 | 1971 | 32.109198612784 | 1970 | 32.457781494975 | 1969 | 33.019960766343 | 1968 | 33.85895285688 | 1967 | 34.61987741946 | 1966 | 35.524888037701 | 1965 | 36.237800212347 | 1964 | 37.046397031185 | 1963 | 37.591677353932 | 1962 | 38.151545515319 | 1961 | 39.142715996931 | 1960 | 40.31295707509 |
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