| Year | Value | | 2020 | 0.54676349293439 | | 2019 | 0.52284336772051 | | 2018 | 0.51784909629127 | | 2017 | 0.55266036281432 | | 2016 | 0.56980629096267 | | 2015 | 0.4770863342574 | | 2014 | 0.49073327622982 | | 2013 | 0.55348214992392 | | 2012 | 0.61186516694435 | | 2011 | 0.61661100724641 | | 2010 | 0.61345045329388 | | 2009 | 0.64435916708845 | | 2008 | 0.67882717671025 | | 2007 | 0.708256930117 | | 2006 | 0.7204644690339 | | 2005 | 0.72237398095605 | | 2004 | 0.73971527619304 | | 2003 | 0.68185563222222 | | 2002 | 0.55499646238269 | | 2001 | 0.56885944079924 | | 2000 | 0.58327351040919 | | 1999 | 0.58947000463332 | | 1998 | 0.6079440861495 | | 1997 | 1.0686908756668 | | 1996 | 1.1072592462982 | | 1995 | 1.1453220428775 | | 1994 | 0.83099798458548 | | 1993 | 0.85831145901336 | | 1992 | 0.88980498091892 | | 1991 | 0.92195389145891 |
|