| Year | Value | | 2020 | 0.72536304420362 | | 2019 | 0.75309144036269 | | 2018 | 0.69868925895021 | | 2017 | 0.85555641111197 | | 2016 | 0.95672288723696 | | 2015 | 1.0004227138227 | | 2014 | 1.0362240579118 | | 2013 | 1.0835779438473 | | 2012 | 1.1381062553098 | | 2011 | 1.1780592030318 | | 2010 | 1.2114894998548 | | 2009 | 1.235214983315 | | 2008 | 1.1798574732172 | | 2007 | 1.1936450338398 | | 2006 | 1.2212174316576 | | 2005 | 1.2353609724762 | | 2004 | 1.2615510770492 | | 2003 | 1.3045341881138 | | 2002 | 1.3153609099792 | | 2001 | 1.3297198723469 | | 2000 | 1.3608704386539 | | 1999 | 1.2298530649233 | | 1998 | 1.2421060889348 | | 1997 | 1.2879023043544 | | 1996 | 1.3388762811372 | | 1995 | 1.292182973109 | | 1994 | 1.3765572303669 | | 1993 | 1.3943403724283 | | 1992 | 1.4151177024149 | | 1991 | 1.4376388219987 |
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