| Year | Value | | 2021 | 26.375982844889 | | 2020 | 26.894210150107 | | 2019 | 26.87441926953 | | 2018 | 26.517046672861 | | 2017 | 26.749338860696 | | 2016 | 27.624901722536 | | 2015 | 27.467657780001 | | 2014 | 26.954828103781 | | 2013 | 28.005503537989 | | 2012 | 23.783146308341 | | 2011 | 23.695590022157 | | 2010 | 23.833178471875 | | 2009 | 23.22207133157 | | 2008 | 23.034450718319 | | 2007 | 21.478093059824 | | 2006 | 21.978414695161 | | 2005 | 21.638910728325 | | 2004 | 21.013508684154 | | 2003 | 21.370881280823 | | 2002 | 21.122478179997 | | 2001 | 21.068822435255 | | 2000 | 20.90785520103 | | 1999 | 36.344124485781 | | 1998 | 36.63029869433 | | 1997 | 34.673097534834 | | 1996 | 34.565916398714 | | 1995 | 41.709890896083 | | 1994 | 41.352173135396 | | 1993 | 40.636737614023 | | 1992 | 42.997674834555 |
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