| Year | Value | | 2020 | 0.26932307798932 | | 2019 | 0.27007022365956 | | 2018 | 0.27629800791872 | | 2017 | 0.55489133008192 | | 2016 | 0.57562041234771 | | 2015 | 0.58412253609753 | | 2014 | 0.59038847561696 | | 2013 | 0.31432500072724 | | 2012 | 0.31866056474569 | | 2011 | 0.42493172165177 | | 2010 | 0.42772303321781 | | 2009 | 0.44519799911286 | | 2008 | 0.3588471627117 | | 2007 | 0.36327234073294 | | 2006 | 0.51583876641562 | | 2005 | 0.60978326895429 | | 2004 | 0.59710779158602 | | 2003 | 1.3717766504513 | | 2002 | 1.5176037669764 | | 2001 | 1.5245320235081 | | 2000 | 1.9678546595589 | | 1999 | 1.9643097975654 | | 1998 | 1.9848142688231 | | 1997 | 1.9734989815237 | | 1996 | 2.1716746397939 | | 1995 | 2.1995582333042 | | 1994 | 1.5652766190383 | | 1993 | 1.5541181689291 | | 1992 | 1.5240855595506 | | 1991 | 1.346824092588 |
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