Year | Value | 2021 | 16.938655908678 | 2020 | 17.226611282316 | 2019 | 17.817696592795 | 2018 | 18.178807189366 | 2017 | 18.700099214957 | 2016 | 19.173894168357 | 2015 | 19.112842682459 | 2014 | 19.642982292904 | 2013 | 19.728088150835 | 2012 | 20.234095546368 | 2011 | 20.119134619468 | 2010 | 20.004531083527 | 2009 | 20.163303721769 | 2008 | 20.341188382324 | 2007 | 20.40437960934 | 2006 | 20.441012460086 | 2005 | 20.611313333461 | 2004 | 20.788549914193 | 2003 | 20.957716679177 | 2002 | 21.241498513807 | 2001 | 21.551350924381 | 2000 | 21.841724454275 | 1999 | 22.071329418964 | 1998 | 22.504469127218 | 1997 | 22.944876989771 | 1996 | 23.300701723704 | 1995 | 23.623792936916 | 1994 | 24.046056260727 | 1993 | 24.411858529435 | 1992 | 24.815857481699 | 1991 | 25.466478137126 | 1990 | 26.052864836421 | 1989 | 26.477584121321 | 1988 | 26.983804330299 | 1987 | 27.462473678062 | 1986 | 27.556297459541 | 1985 | 27.440647262591 | 1984 | 27.438372632477 | 1983 | 27.679348201438 | 1982 | 28.276819030966 | 1981 | 28.070905518486 | 1980 | 27.588643342633 | 1979 | 27.535168183885 | 1978 | 27.621278657151 | 1977 | 27.892856330789 | 1976 | 28.291014674388 | 1975 | 29.115309957388 | 1974 | 29.794635896724 | 1973 | 30.654805284133 | 1972 | 31.288465627981 | 1971 | 31.759795113969 | 1970 | 32.492257121528 | 1969 | 32.747501196308 | 1968 | 33.23907986721 | 1967 | 33.124993077202 | 1966 | 33.406894248203 | 1965 | 34.474214335355 | 1964 | 35.131801644445 | 1963 | 36.27460978714 | 1962 | 35.103311241586 | 1961 | 31.165343415489 | 1960 | 31.908379711819 |
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