Year | Value | 2021 | 16.401257514457 | 2020 | 16.792599459739 | 2019 | 17.510379272158 | 2018 | 17.951438450123 | 2017 | 18.598997750938 | 2016 | 19.166013260616 | 2015 | 19.054322732711 | 2014 | 19.727119325896 | 2013 | 19.833668269101 | 2012 | 20.418002745119 | 2011 | 20.246018368954 | 2010 | 20.048785846831 | 2009 | 20.227761675944 | 2008 | 20.407968226972 | 2007 | 20.494548604084 | 2006 | 20.57852667432 | 2005 | 20.866917801184 | 2004 | 21.089078826535 | 2003 | 21.312770219966 | 2002 | 21.688527227107 | 2001 | 22.070508119472 | 2000 | 22.381504868101 | 1999 | 22.716680986809 | 1998 | 23.279359124101 | 1997 | 23.826168034282 | 1996 | 24.263409831066 | 1995 | 24.679545357321 | 1994 | 25.197503358055 | 1993 | 25.639303987878 | 1992 | 26.125463475542 | 1991 | 26.95623853871 | 1990 | 27.688626904496 | 1989 | 28.296150591621 | 1988 | 28.967069168858 | 1987 | 29.667025835839 | 1986 | 29.821874697537 | 1985 | 29.643547181238 | 1984 | 29.665944652676 | 1983 | 29.99144587846 | 1982 | 30.763717242337 | 1981 | 30.487280161576 | 1980 | 29.777891532547 | 1979 | 29.718260661249 | 1978 | 29.933497606176 | 1977 | 30.271535135267 | 1976 | 30.81150789046 | 1975 | 31.914637936799 | 1974 | 32.734428265858 | 1973 | 33.91574169855 | 1972 | 34.662176596428 | 1971 | 35.100975873601 | 1970 | 36.06277326826 | 1969 | 36.435260595517 | 1968 | 37.115738942689 | 1967 | 36.872531007537 | 1966 | 37.512698150011 | 1965 | 38.726321763432 | 1964 | 39.469216659816 | 1963 | 41.104282102872 | 1962 | 39.442291648474 | 1961 | 33.689082013479 | 1960 | 34.686704373181 |
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