| Year | Value | | 2020 | 0.35171589484242 | | 2019 | 0.34684693972128 | | 2018 | 0.35587699396798 | | 2017 | 0.3574090524267 | | 2016 | 0.3395782357819 | | 2015 | 0.34281136502458 | | 2014 | 0.35840542668702 | | 2013 | 0.3365383359424 | | 2012 | 0.34168097930324 | | 2011 | 0.34313817145272 | | 2010 | 0.34605484310864 | | 2009 | 0.34981983921658 | | 2008 | 0.34293231239526 | | 2007 | 0.34815535867128 | | 2006 | 0.35485574060666 | | 2005 | 0.3984498169572 | | 2004 | 0.40172590501774 | | 2003 | 0.35273475657608 | | 2002 | 0.36089462966528 | | 2001 | 0.39853695335924 | | 2000 | 0.42002536217377 | | 1999 | 0.43605060705476 | | 1998 | 0.4438230146756 | | 1997 | 0.46840453554759 | | 1996 | 0.52229171130908 | | 1995 | 0.50067061422628 | | 1994 | 0.49955077064365 | | 1993 | 0.51105275994379 | | 1992 | 0.55472110618424 | | 1991 | 0.58093804471386 |
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