Year | Value | 2022 | 17.616 | 2021 | 17.742 | 2020 | 17.889 | 2019 | 18.056 | 2018 | 18.243 | 2017 | 18.452 | 2016 | 18.681 | 2015 | 18.914 | 2014 | 19.149 | 2013 | 19.385 | 2012 | 19.624 | 2011 | 19.857 | 2010 | 20.078 | 2009 | 20.3 | 2008 | 20.524 | 2007 | 20.75 | 2006 | 20.981 | 2005 | 21.218 | 2004 | 21.457 | 2003 | 21.698 | 2002 | 21.941 | 2001 | 22.068 | 2000 | 21.977 | 1999 | 21.886 | 1998 | 21.796 | 1997 | 21.705 | 1996 | 21.616 | 1995 | 21.526 | 1994 | 21.436 | 1993 | 21.347 | 1992 | 21.258 | 1991 | 21.2 | 1990 | 21.2 | 1989 | 21.2 | 1988 | 21.2 | 1987 | 21.2 | 1986 | 21.2 | 1985 | 21.2 | 1984 | 21.2 | 1983 | 21.2 | 1982 | 21.2 | 1981 | 21.193 | 1980 | 21.173 | 1979 | 21.153 | 1978 | 21.133 | 1977 | 21.113 | 1976 | 21.073 | 1975 | 20.992 | 1974 | 20.912 | 1973 | 20.832 | 1972 | 20.752 | 1971 | 20.611 | 1970 | 20.353 | 1969 | 20.097 | 1968 | 19.844 | 1967 | 19.593 | 1966 | 19.382 | 1965 | 19.301 | 1964 | 19.221 | 1963 | 19.141 | 1962 | 19.061 | 1961 | 18.986 | 1960 | 18.926 |
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