| Year | Value | | 2020 | 0.24741448279759 | | 2019 | 0.25323710421243 | | 2018 | 0.26143594716993 | | 2017 | 0.27018087669935 | | 2016 | 0.27958671734561 | | 2015 | 0.28937745682509 | | 2014 | 0.29946199699227 | | 2013 | 0.31004100134976 | | 2012 | 0.32129158846049 | | 2011 | 0.33316169068356 | | 2010 | 0.34534172426971 | | 2009 | 0.35758453512184 | | 2008 | 0.3698183227292 | | 2007 | 0.38224695563152 | | 2005 | 0.54087460310001 | | 2004 | 0.55806459763297 | | 2003 | 0.51670554525909 | | 2002 | 0.83369316961294 | | 2001 | 0.86462943762926 | | 2000 | 1.2499660470216 | | 1999 | 1.1940277045241 | | 1998 | 0.45513492323088 | | 1997 | 0.47046318433477 | | 1996 | 0.48684833980456 | | 1995 | 0.50460559837204 | | 1994 | 0.52331122561452 | | 1993 | 0.53977483832394 | | 1992 | 0.5567852260381 | | 1991 | 0.57794854658944 |
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