| Year | Value | | 2017 | 0.69966543819792 | | 2016 | 0.7111100540044 | | 2015 | 0.71745641078578 | | 2014 | 0.72938528957551 | | 2013 | 0.72075901011143 | | 2012 | 0.7303027278201 | | 2011 | 0.74988390925156 | | 2010 | 0.74845057471496 | | 2009 | 0.7477123656962 | | 2008 | 0.77060005803548 | | 2007 | 0.78340735826607 | | 2006 | 0.82965924860337 | | 2005 | 0.74957136045765 | | 2004 | 0.7868571355727 | | 2003 | 0.79437520991442 | | 2002 | 0.81056487269026 | | 2001 | 0.83629177345422 | | 2000 | 0.85677594017383 | | 1999 | 0.88368575690421 | | 1998 | 0.94260107722369 | | 1997 | 0.97030316701938 | | 1996 | 0.97600921733583 | | 1995 | 0.97773257867587 | | 1994 | 0.43798161794109 | | 1993 | 0.45094381779335 | | 1992 | 0.46417469879688 | | 1991 | 0.47638504430009 | | 1990 | 0.49105560525575 |
|