| Year | Value | | 2020 | 1.6971160882521 | | 2019 | 1.9184041685128 | | 2018 | 1.9393717410887 | | 2017 | 1.9663565791838 | | 2016 | 1.9979836603061 | | 2015 | 2.0144487603959 | | 2014 | 1.9403463246775 | | 2013 | 1.9645866604501 | | 2012 | 1.9081122815613 | | 2011 | 1.9591849522861 | | 2010 | 2.0169191353416 | | 2009 | 2.0608703719589 | | 2008 | 2.0405909789792 | | 2007 | 2.0912395076764 | | 2006 | 2.0447020152491 | | 2005 | 1.7437551767732 | | 2004 | 1.7456253900382 | | 2003 | 1.5994796807531 | | 2002 | 1.4275266828167 | | 2001 | 1.4374302119695 | | 2000 | 1.3831102969986 | | 1999 | 1.3260622260727 | | 1998 | 1.3579937548585 | | 1997 | 1.3882345072613 | | 1996 | 1.4256547333112 | | 1995 | 1.4616295930019 | | 1994 | 0.94179494376097 | | 1993 | 0.92455633601118 | | 1992 | 0.95246187411606 | | 1991 | 0.77464472328212 |
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