| Year | Value | | 2020 | 0.20150183346518 | | 2019 | 0.2085720034356 | | 2018 | 0.21314065804496 | | 2017 | 0.22663690772977 | | 2016 | 0.22957442448465 | | 2015 | 0.1067809180615 | | 2014 | 0.10877998448286 | | 2013 | 0.11075111569534 | | 2012 | 0.112664761859 | | 2011 | 0.11452155169292 | | 2010 | 0.090121662544026 | | 2009 | 0.090993091735801 | | 2008 | 0.12131791463517 | | 2007 | 0.12256985562497 | | 2006 | 0.12396726414165 | | 2005 | 0.12541159638033 | | 2004 | 0.11020259277313 | | 2003 | 0.12795500800848 | | 2002 | 0.13097554243617 | | 2001 | 0.13403932634988 | | 2000 | 0.12113398367477 | | 1999 | 0.1240704025092 | | 1998 | 0.12708517650966 | | 1997 | 0.13015740585877 | | 1996 | 0.24010698099931 | | 1995 | 0.21659540297917 | | 1994 | 0.2282779283778 | | 1993 | 0.22550558351825 | | 1992 | 0.22855001017047 | | 1991 | 0.18800844533937 |
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