| Year | Value | | 2020 | 0.44159855438297 | | 2019 | 0.43422381352575 | | 2018 | 0.43656017929474 | | 2017 | 0.4458855945204 | | 2016 | 0.45403204413631 | | 2015 | 0.46032133614878 | | 2014 | 0.46062687299612 | | 2013 | 0.46590323120105 | | 2012 | 0.46794388703335 | | 2011 | 0.48160289599935 | | 2010 | 0.48481053579914 | | 2009 | 0.49281255476409 | | 2008 | 0.48973868345242 | | 2007 | 0.50271484295737 | | 2006 | 0.4786957848865 | | 2005 | 0.50821968630188 | | 2004 | 0.5134450523941 | | 2003 | 0.5351751345651 | | 2002 | 0.51722007521132 | | 2001 | 0.53329504336813 | | 2000 | 0.54174570624532 | | 1999 | 0.60169083690164 | | 1998 | 0.63098442538118 | | 1997 | 0.63738862752438 | | 1996 | 0.64593642821103 | | 1995 | 0.63587169378735 | | 1994 | 0.74001573615001 | | 1993 | 0.78877087226923 | | 1992 | 0.79154462716968 | | 1991 | 0.79783589360436 |
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