| Year | Value | | 2020 | 0.34559014874546 | | 2019 | 0.31754958977886 | | 2018 | 0.33637706867424 | | 2017 | 0.32846091971977 | | 2016 | 0.34054326488666 | | 2015 | 0.35301263745799 | | 2014 | 0.34344891399433 | | 2013 | 0.35484249376625 | | 2012 | 0.35921607708315 | | 2011 | 0.36023160996565 | | 2010 | 0.41337642168925 | | 2009 | 0.41720346443203 | | 2008 | 0.39114193889059 | | 2007 | 0.39476108182081 | | 2006 | 0.40067277410692 | | 2005 | 0.41008368441053 | | 2004 | 0.37427250781294 | | 2003 | 0.41357467499523 | | 2002 | 0.4267944499061 | | 2001 | 0.46561390687519 | | 2000 | 0.47335524487902 | | 1999 | 0.49486364766954 | | 1998 | 0.49960580840143 | | 1997 | 0.50119446975199 | | 1996 | 0.52385587647404 | | 1995 | 0.55196535187791 | | 1994 | 0.56019082340208 | | 1993 | 0.63253398288823 | | 1992 | 0.63905410696836 | | 1991 | 0.64195790156801 |
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