| Year | Value | | 2020 | 0.54059167759112 | | 2019 | 0.5007531565929 | | 2018 | 0.5013946672514 | | 2017 | 0.50055213342034 | | 2016 | 0.51245601366818 | | 2015 | 0.53983105341373 | | 2014 | 0.57838952227864 | | 2013 | 0.86017939472001 | | 2012 | 0.86891425821458 | | 2011 | 0.90501896331039 | | 2010 | 0.9119667515504 | | 2009 | 0.91337105352565 | | 2008 | 0.89003604645988 | | 2007 | 0.90809248797594 | | 2006 | 0.8981149599666 | | 2005 | 0.76848793049631 | | 2004 | 0.76489427861725 | | 2003 | 1.0458730775305 | | 2002 | 1.0817195723409 | | 2001 | 1.1186224258356 | | 2000 | 1.1177490622414 | | 1999 | 1.1092219128268 | | 1998 | 1.1098235927951 | | 1997 | 1.1729470207003 | | 1996 | 1.2153747874947 | | 1995 | 1.2430969139145 | | 1994 | 1.2638704235695 | | 1993 | 1.2983693847233 | | 1992 | 1.3301115076814 | | 1991 | 1.2692279047179 |
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