| Year | Value | | 2022 | 19.813734749888 | | 2021 | 18.904798753831 | | 2020 | 17.075666923139 | | 2019 | 17.421769127989 | | 2018 | 15.699416453685 | | 2017 | 16.573751613727 | | 2016 | 16.166446204055 | | 2015 | 15.589588360315 | | 2014 | 15.316266378732 | | 2013 | 15.020425367363 | | 2012 | 15.00919379176 | | 2011 | 14.51971694756 | | 2010 | 13.678340363426 | | 2009 | 13.13760723257 | | 2008 | 13.201705933099 | | 2007 | 13.862105147864 | | 2006 | 13.684175095508 | | 2005 | 12.899803481681 | | 2004 | 12.188179180118 | | 2003 | 11.720815896043 | | 2002 | 10.395499106183 | | 2001 | 9.8025080665 | | 2000 | 10.646870112031 | | 1999 | 10.718946374596 | | 1998 | 11.036483063754 | | 1997 | 10.589091758038 | | 1996 | 9.4944412884239 | | 1995 | 9.4027344016103 | | 1994 | 8.9936659409003 | | 1993 | 18.98088283176 | | 1992 | 19.849509147702 | | 1991 | 18.239367374354 | | 1990 | 26.265837346995 |
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