| Year | Value | | 2021 | 23.412381422925 | | 2020 | 23.979249011858 | | 2019 | 24.545454545455 | | 2018 | 25.112648221344 | | 2017 | 25.678853754941 | | 2016 | 26.245059288538 | | 2015 | 26.812252964427 | | 2014 | 27.378656126482 | | 2013 | 27.945059288538 | | 2012 | 28.511462450593 | | 2011 | 29.077865612648 | | 2010 | 29.644268774704 | | 2009 | 30.210770750988 | | 2008 | 30.777272727273 | | 2007 | 31.343774703557 | | 2006 | 31.910276679842 | | 2005 | 32.476778656126 | | 2004 | 33.043280632411 | | 2003 | 33.609782608696 | | 2002 | 34.17628458498 | | 2001 | 34.742786561265 | | 2000 | 35.309288537549 | | 1999 | 35.875790513834 | | 1998 | 36.442292490119 | | 1997 | 37.008794466403 | | 1996 | 37.575296442688 | | 1995 | 38.141798418972 | | 1994 | 38.708300395257 | | 1993 | 39.274802371541 | | 1992 | 39.841304347826 | | 1991 | 40.407806324111 | | 1990 | 40.974308300395 |
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