| Year | Value | | 2021 | 9.4099690757803 | | 2020 | 9.532311027513 | | 2019 | 9.6546529792457 | | 2018 | 9.7769949309784 | | 2017 | 9.8993368827111 | | 2016 | 10.021678834444 | | 2015 | 10.144020786177 | | 2014 | 10.266362737909 | | 2013 | 10.388704689642 | | 2012 | 10.511046641375 | | 2011 | 10.633388593107 | | 2010 | 10.75573054484 | | 2009 | 10.878072496573 | | 2008 | 11.000414448306 | | 2007 | 11.122756400038 | | 2006 | 11.245098351771 | | 2005 | 11.367440303504 | | 2004 | 11.489782255236 | | 2003 | 11.612124206969 | | 2002 | 11.734466158702 | | 2001 | 11.856808110434 | | 2000 | 11.979150062167 | | 1999 | 12.1014920139 | | 1998 | 12.223833965633 | | 1997 | 12.346175917365 | | 1996 | 12.468517869098 | | 1995 | 12.590859820831 | | 1994 | 12.713201772563 | | 1993 | 12.835543724296 | | 1992 | 12.957885676029 | | 1991 | 13.080227627762 | | 1990 | 13.202569579494 |
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