| Year | Value | | 2021 | 12.488751814223 | | 2020 | 12.601596516691 | | 2019 | 12.714441219158 | | 2018 | 12.827285921625 | | 2017 | 12.940130624093 | | 2016 | 13.05297532656 | | 2015 | 13.165820029028 | | 2014 | 13.278519593614 | | 2013 | 13.3912191582 | | 2012 | 13.503918722787 | | 2011 | 13.616618287373 | | 2010 | 13.729317851959 | | 2009 | 13.737554426705 | | 2008 | 13.745791001451 | | 2007 | 13.754027576197 | | 2006 | 13.762264150943 | | 2005 | 13.770500725689 | | 2004 | 13.778737300435 | | 2003 | 13.786973875181 | | 2002 | 13.795210449927 | | 2001 | 13.803447024673 | | 2000 | 13.811683599419 | | 1999 | 13.819920174165 | | 1998 | 13.828156748911 | | 1997 | 13.836393323658 | | 1996 | 13.844629898404 | | 1995 | 13.85286647315 | | 1994 | 13.861103047896 | | 1993 | 13.869339622641 | | 1992 | 13.877576197387 | | 1991 | 13.885812772133 | | 1990 | 13.89404934688 |
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