| Year | Value | | 2021 | 11.41935483871 | | 2020 | 11.344913151365 | | 2019 | 11.27047146402 | | 2018 | 11.196029776675 | | 2017 | 11.12158808933 | | 2016 | 11.047146401985 | | 2015 | 10.97270471464 | | 2014 | 10.898263027295 | | 2013 | 10.82382133995 | | 2012 | 10.749379652605 | | 2011 | 10.674937965261 | | 2010 | 10.600496277916 | | 2009 | 10.526054590571 | | 2008 | 10.451612903226 | | 2007 | 10.377171215881 | | 2006 | 10.302729528536 | | 2005 | 10.228287841191 | | 2004 | 10.153846153846 | | 2003 | 10.079404466501 | | 2002 | 10.004962779156 | | 2001 | 9.9305210918114 | | 2000 | 9.8560794044665 | | 1999 | 9.2521091811414 | | 1998 | 8.6481389578164 | | 1997 | 8.0441687344913 | | 1996 | 7.4401985111663 | | 1995 | 6.8362282878412 | | 1994 | 6.2322580645161 | | 1993 | 5.6282878411911 | | 1992 | 5.024317617866 | | 1991 | 4.4203473945409 | | 1990 | 3.8163771712159 |
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