| Year | Value | | 2021 | 11.176574658945 | | 2020 | 10.567583210184 | | 2019 | 11.405770110906 | | 2018 | 11.456981978636 | | 2017 | 11.419122418247 | | 2016 | 11.296120252397 | | 2015 | 11.478728958621 | | 2014 | 11.482563203902 | | 2013 | 11.611503370267 | | 2012 | 11.622986110858 | | 2011 | 11.481385229956 | | 2010 | 11.190297925441 | | 2009 | 11.614937053559 | | 2008 | 11.47230108895 | | 2007 | 11.334040127223 | | 2006 | 10.851627618361 | | 2005 | 10.656816602646 | | 2004 | 10.426294574192 | | 2003 | 10.99852141239 | | 2002 | 10.835304714938 | | 2001 | 10.961685400499 | | 2000 | 11.705000734914 | | 1999 | 11.508536135335 | | 1998 | 10.834979795673 | | 1997 | 10.729367972873 | | 1996 | 10.901851794023 | | 1995 | 11.476134930144 | | 1994 | 11.677844278648 | | 1993 | 11.460457253168 | | 1992 | 11.75387471652 | | 1991 | 11.629713709169 | | 1990 | 9.8322836818383 | | 1989 | 10.250721937674 | | 1988 | 9.8164739733434 | | 1987 | 10.084634391165 | | 1986 | 9.9378834222969 | | 1985 | 10.196980845149 | | 1984 | 10.190858256491 | | 1983 | 9.7504031100984 | | 1982 | 9.7944266111617 | | 1981 | 10.056736961121 | | 1980 | 10.28256689631 | | 1979 | 10.379879002728 | | 1978 | 10.493259791897 | | 1977 | 10.490865794144 | | 1976 | 10.170334296747 | | 1975 | 10.044877804063 | | 1974 | 10.475225573993 | | 1973 | 10.919394810092 | | 1972 | 10.784103450872 |
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