| Year | Value | | 2020 | 0.37881877629053 | | 2019 | 0.37801143132638 | | 2018 | 0.381871834103 | | 2017 | 0.38824793435736 | | 2016 | 0.39131889135784 | | 2015 | 0.39326963374427 | | 2014 | 0.39379222779343 | | 2013 | 0.39502148252414 | | 2012 | 0.39652674924731 | | 2011 | 0.39518894991611 | | 2010 | 0.39313824275954 | | 2009 | 0.39181094037951 | | 2008 | 0.36267205923052 | | 2007 | 0.36177598702318 | | 2006 | 0.37734567505255 | | 2005 | 0.40800060996091 | | 2004 | 0.37699987166984 | | 2003 | 0.37718710167935 | | 2002 | 0.37584372331515 | | 2001 | 0.3727852677155 | | 2000 | 0.36671868262263 | | 1999 | 0.37450329220902 | | 1998 | 0.37335807136066 | | 1997 | 0.36315449724604 | | 1996 | 0.36597640805172 | | 1995 | 0.3744340648708 | | 1994 | 0.34807744056776 | | 1993 | 0.36311314242405 | | 1992 | 0.3652643724663 | | 1991 | 0.38225593631237 |
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