| Year | Value | | 2020 | 3.2988226473119 | | 2019 | 2.9786965015687 | | 2018 | 2.7085872798424 | | 2017 | 2.5830215508341 | | 2016 | 2.0222833401187 | | 2015 | 1.9677726365696 | | 2014 | 1.982776036094 | | 2013 | 0.86779681480839 | | 2012 | 0.8757825783694 | | 2011 | 0.88365960479208 | | 2010 | 0.89624575900404 | | 2009 | 0.90989146972791 | | 2008 | 0.92346580410142 | | 2007 | 0.94000926276954 | | 2005 | 0.70111207490271 | | 2004 | 0.72031547006602 | | 2003 | 0.95664395129383 | | 2002 | 0.97341729558237 | | 2001 | 0.99151888829358 | | 2000 | 0.76311455837112 | | 1999 | 0.78345291899186 | | 1998 | 0.80100346469486 | | 1997 | 0.82203828450808 | | 1996 | 0.84609354860095 | | 1995 | 0.87985889702868 | | 1994 | 0.84894937986512 | | 1993 | 0.87178840416808 | | 1992 | 0.89659380427381 | | 1991 | 0.8997118333921 |
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