| Year | Value | | 2020 | 0.78445542813456 | | 2019 | 0.77558427148273 | | 2018 | 0.79078319086576 | | 2017 | 0.78810344791694 | | 2016 | 0.78865149001496 | | 2015 | 0.79166037394627 | | 2014 | 0.78493787306561 | | 2013 | 0.78421150502891 | | 2012 | 0.79313383460993 | | 2011 | 0.79081737940785 | | 2010 | 0.79940874611947 | | 2009 | 0.80328494834409 | | 2008 | 0.7926012604607 | | 2007 | 0.79807085165475 | | 2006 | 0.8643131776807 | | 2005 | 0.88663920665375 | | 2004 | 0.88914389959182 | | 2003 | 0.90217780991692 | | 2002 | 0.91476226737538 | | 2001 | 0.93933419587841 | | 2000 | 0.96386146302952 | | 1999 | 0.97676756974634 | | 1998 | 1.0189902558033 | | 1997 | 1.0288327570078 | | 1996 | 1.0769841988958 | | 1995 | 1.1241695062873 | | 1994 | 0.84548423033968 | | 1993 | 0.88190719805691 | | 1992 | 0.96277417836 | | 1991 | 0.87289785739722 |
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