| Year | Value | | 2021 | 9.0982214675127 | | 2020 | 9.0982214675127 | | 2019 | 9.0982214675127 | | 2018 | 9.0982214675127 | | 2017 | 9.0982214675127 | | 2016 | 9.0982214675127 | | 2015 | 9.0982214675127 | | 2014 | 9.0982214675127 | | 2013 | 9.0982214675127 | | 2012 | 9.0982214675127 | | 2011 | 9.0982214675127 | | 2010 | 9.0982214675127 | | 2009 | 9.0982214675127 | | 2008 | 9.0982214675127 | | 2007 | 9.3842166413442 | | 2006 | 9.3842166413442 | | 2005 | 9.3842166413442 | | 2004 | 9.3842166413442 | | 2003 | 9.5450889266244 | | 2002 | 9.5450889266244 | | 2001 | 9.5450889266244 | | 2000 | 9.5450889266244 | | 1999 | 13.120028599517 | | 1998 | 13.584770756993 | | 1997 | 13.584770756993 | | 1996 | 14.299758691572 | | 1995 | 14.299758691572 | | 1994 | 14.746626150684 | | 1993 | 15.041558673697 | | 1992 | 13.540084011082 | | 1991 | 13.334524979891 | | 1990 | 13.066404504424 | | 1989 | 12.923406917508 | | 1988 | 12.789346679775 | | 1987 | 12.878720171597 | | 1986 | 12.968093663419 | | 1985 | 13.003843060148 | | 1984 | 13.084279202788 | | 1983 | 13.111091250335 | | 1982 | 13.191527392975 | | 1981 | 13.236214138886 | | 1980 | 13.263026186433 | | 1979 | 13.352399678255 | | 1978 | 13.441773170078 | | 1977 | 13.432835820895 | | 1976 | 12.85190812405 | | 1975 | 12.628474394495 | | 1974 | 12.36929126821 | | 1973 | 12.315667173117 | | 1972 | 12.226293681294 | | 1971 | 11.913486459916 | | 1970 | 11.886674412369 | | 1969 | 11.868799714005 | | 1968 | 11.904549110734 | | 1967 | 11.886674412369 | | 1966 | 11.833050317276 | | 1965 | 11.779426222183 | | 1964 | 11.734739476271 | | 1963 | 11.707927428725 | | 1962 | 11.663240682814 | | 1961 | 11.573867190991 |
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