Year | Value | 2021 | 13.902 | 2020 | 14.125 | 2019 | 14.783 | 2018 | 15.187 | 2017 | 16.206 | 2016 | 16.824 | 2015 | 17.346 | 2014 | 17.504 | 2013 | 17.632 | 2012 | 17.729 | 2011 | 17.806 | 2010 | 17.87 | 2009 | 17.849 | 2008 | 17.812 | 2007 | 18.005 | 2006 | 18.194 | 2005 | 18.353 | 2004 | 18.352 | 2003 | 18.453 | 2002 | 18.756 | 2001 | 18.983 | 2000 | 19.366 | 1999 | 19.674 | 1998 | 19.738 | 1997 | 19.985 | 1996 | 20.449 | 1995 | 20.974 | 1994 | 21.419 | 1993 | 21.57 | 1992 | 21.683 | 1991 | 21.844 | 1990 | 21.989 | 1989 | 21.907 | 1988 | 22.069 | 1987 | 22.232 | 1986 | 22.404 | 1985 | 22.61 | 1984 | 22.876 | 1983 | 23.209 | 1982 | 23.617 | 1981 | 24.104 | 1980 | 24.573 | 1979 | 24.985 | 1978 | 25.257 | 1977 | 25.37 | 1976 | 25.305 | 1975 | 25.092 | 1974 | 24.739 | 1973 | 24.343 | 1972 | 23.94 | 1971 | 23.635 | 1970 | 23.472 | 1969 | 23.185 | 1968 | 22.987 | 1967 | 23.061 | 1966 | 23.141 | 1965 | 23.259 | 1964 | 23.437 | 1963 | 23.663 | 1962 | 23.798 | 1961 | 23.638 | 1960 | 23.784 |
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