Year | Value | 2021 | 22.958977807666 | 2020 | 22.958977807666 | 2019 | 22.958977807666 | 2018 | 23.006052454607 | 2017 | 22.972427706792 | 2016 | 22.938802958978 | 2015 | 22.905178211163 | 2014 | 22.871553463349 | 2013 | 22.837928715535 | 2012 | 22.80430396772 | 2011 | 22.770679219906 | 2010 | 22.730329522529 | 2009 | 22.75722932078 | 2008 | 22.649630127774 | 2007 | 22.340282447882 | 2006 | 22.367182246133 | 2005 | 22.394082044385 | 2004 | 22.420981842636 | 2003 | 22.447881640888 | 2002 | 22.609280430397 | 2001 | 22.636180228648 | 2000 | 22.6630800269 | 1999 | 22.6630800269 | 1998 | 22.932078009415 | 1997 | 23.066577000672 | 1996 | 22.999327505044 | 1995 | 22.864828513786 | 1994 | 22.864828513786 | 1993 | 22.528581035642 | 1992 | 22.192333557498 | 1991 | 22.192333557498 | 1990 | 21.385339609953 | 1989 | 20.511096166779 | 1988 | 20.376597175521 | 1987 | 20.107599193006 | 1986 | 19.838601210491 | 1985 | 19.636852723605 | 1984 | 19.435104236718 | 1983 | 19.233355749832 | 1982 | 19.098856758574 | 1981 | 18.964357767317 | 1980 | 18.76260928043 | 1979 | 18.560860793544 | 1978 | 18.2246133154 | 1977 | 17.619367854741 | 1976 | 17.350369872226 | 1975 | 17.14862138534 | 1974 | 16.812373907196 | 1973 | 16.812373907196 | 1972 | 16.476126429052 | 1971 | 16.341627437794 | 1970 | 16.341627437794 | 1969 | 15.669132481506 | 1968 | 15.601882985878 | 1967 | 15.601882985878 | 1966 | 15.46738399462 | 1965 | 15.46738399462 | 1964 | 15.46738399462 | 1963 | 15.46738399462 | 1962 | 15.46738399462 | 1961 | 15.46738399462 |
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