Year | Value | 2021 | 20.695459559712 | 2020 | 20.699854526596 | 2019 | 20.487138525095 | 2018 | 20.275059330228 | 2017 | 20.062979695878 | 2016 | 19.850900501011 | 2015 | 19.638821306144 | 2014 | 19.426742111277 | 2013 | 19.214662476927 | 2012 | 19.00258328206 | 2011 | 18.790504087194 | 2010 | 18.578424892327 | 2009 | 18.36634569746 | 2008 | 18.15426606311 | 2007 | 17.942186868243 | 2006 | 17.730107673376 | 2005 | 17.518028478509 | 2004 | 17.305949283642 | 2003 | 17.093869649292 | 2002 | 16.881790454426 | 2001 | 16.669711259559 | 2000 | 16.457632064692 | 1999 | 16.245552430342 | 1998 | 16.033473235475 | 1997 | 15.821394040608 | 1996 | 14.06346136943 | 1995 | 13.18449503384 | 1994 | 12.305528698251 | 1993 | 12.305528698251 | 1992 | 12.305528698251 | 1991 | 12.305528698251 | 1990 | 11.866045530456 | 1989 | 11.426562362661 | 1988 | 11.426562362661 | 1987 | 10.987079194867 | 1986 | 10.547596027072 | 1985 | 10.547596027072 | 1984 | 10.108112859277 | 1983 | 9.2291465236881 | 1982 | 9.2291465236881 | 1981 | 8.3501801880988 | 1980 | 8.3501801880988 | 1979 | 8.3501801880988 | 1978 | 8.3501801880988 | 1977 | 7.9106970203041 | 1976 | 7.9106970203041 | 1975 | 7.9106970203041 | 1974 | 7.4712138525095 | 1973 | 7.4712138525095 | 1972 | 7.4712138525095 | 1971 | 7.4712138525095 | 1970 | 7.4712138525095 | 1969 | 7.4712138525095 | 1968 | 7.4712138525095 | 1967 | 7.4712138525095 | 1966 | 7.4712138525095 | 1965 | 7.4712138525095 | 1964 | 7.4712138525095 | 1963 | 7.4712138525095 | 1962 | 7.4712138525095 | 1961 | 7.4712138525095 |
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