| Year | Value | | 2020 | 0.31436925461293 | | 2019 | 0.3209578590827 | | 2018 | 0.33448204580109 | | 2017 | 0.24010677548306 | | 2016 | 0.24096938895827 | | 2015 | 0.24868135119418 | | 2014 | 0.25520704881869 | | 2013 | 0.25999900707276 | | 2012 | 0.26397268883946 | | 2011 | 0.26692581195712 | | 2010 | 0.27245642840391 | | 2009 | 0.27251395896718 | | 2008 | 0.2732189480429 | | 2007 | 0.27573114007993 | | 2005 | 0.29234239598998 | | 2004 | 0.30095829045223 | | 2003 | 0.43270022056927 | | 2002 | 0.44601142817445 | | 2001 | 0.4454067394193 | | 2000 | 0.3259875505207 | | 1999 | 0.33550271514301 | | 1998 | 0.34541650275012 | | 1997 | 0.35587177151035 | | 1996 | 0.36675378590308 | | 1995 | 0.40353586330941 | | 1994 | 0.21129078066133 | | 1993 | 0.21761317517208 | | 1992 | 0.22411164943559 | | 1991 | 0.46142328318816 |
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