| Year | Value | | 2020 | 12.364760432767 | | 2019 | 12.542618513774 | | 2018 | 12.807604701772 | | 2017 | 13.076329513146 | | 2016 | 13.212829706764 | | 2015 | 13.290864054389 | | 2014 | 13.371030692729 | | 2013 | 13.484962011509 | | 2012 | 13.74319737275 | | 2011 | 14.020513383596 | | 2010 | 14.394253428757 | | 2009 | 14.752573565436 | | 2008 | 15.246801945552 | | 2007 | 15.758916660295 | | 2005 | 16.190515884339 | | 2004 | 16.401268038335 | | 2003 | 17.222284271706 | | 2002 | 15.360530928456 | | 2001 | 15.874657619005 | | 2000 | 18.946498876473 | | 1999 | 19.103127277451 | | 1998 | 4.5177429317946 | | 1997 | 4.4167618030758 | | 1996 | 5.2669783441003 | | 1995 | 5.5797796900077 | | 1994 | 6.0129858629236 | | 1993 | 6.2311790070446 |
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