Year | Value | 2021 | 20.191261597633 | 2020 | 20.2886384681 | 2019 | 20.199558675113 | 2018 | 20.2370889465 | 2017 | 20.190466176978 | 2016 | 20.134095522904 | 2015 | 19.991896582789 | 2014 | 20.015226865222 | 2013 | 20.013628603766 | 2012 | 19.958095973076 | 2011 | 19.973124214715 | 2010 | 19.693513174616 | 2009 | 19.888027507383 | 2008 | 19.665321670152 | 2007 | 19.76780349748 | 2006 | 19.827504326662 | 2005 | 19.735975390764 | 2004 | 19.743948556825 | 2003 | 19.886585079342 | 2002 | 19.88282330045 | 2001 | 19.88789193131 | 2000 | 19.624903109293 | 1999 | 19.725427235505 | 1998 | 19.368604627212 | 1997 | 19.222086937018 | 1996 | 19.029361212257 | 1995 | 19.072619164777 | 1994 | 18.591179048696 | 1993 | 18.278573341237 | 1992 | 18.25108882974 | 1991 | 18.718136801243 | 1990 | 18.422802404684 | 1989 | 18.604652165204 | 1988 | 18.322984201198 | 1987 | 18.527881804375 | 1986 | 18.192912217892 | 1985 | 18.533939152681 | 1984 | 18.367659997414 | 1983 | 18.065984274728 | 1982 | 18.547808426535 | 1981 | 17.990324470014 | 1980 | 18.180538898623 | 1979 | 17.859846804108 | 1978 | 17.779547004668 | 1977 | 17.624626962173 | 1976 | 17.522192105924 | 1975 | 17.553886058971 | 1974 | 17.356445409068 | 1973 | 17.463875232317 | 1972 | 17.202463507583 | 1971 | 17.149978321336 | 1970 | 17.181925826008 | 1969 | 17.08709751849 | 1968 | 17.39516274211 | 1967 | 17.41139004607 | 1966 | 17.334817455508 | 1965 | 17.220212121289 | 1964 | 16.940798231224 | 1963 | 16.759508819793 | 1962 | 16.687246606845 | 1961 | 16.596475125318 |
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