| Year | Value | | 2020 | 0.66068484703573 | | 2019 | 0.64270990982168 | | 2018 | 0.57699012867344 | | 2017 | 0.53147704034817 | | 2016 | 0.52949726526517 | | 2015 | 0.51647507824995 | | 2014 | 0.51594852401169 | | 2013 | 0.42868901374567 | | 2012 | 0.41900893681835 | | 2011 | 0.4261768685851 | | 2010 | 0.48490368432991 | | 2009 | 0.48246892580399 | | 2008 | 0.5198422036319 | | 2007 | 0.50723840064612 | | 2006 | 0.47700242750679 | | 2005 | 0.48253955516803 | | 2004 | 0.34441749073492 | | 2003 | 0.48968017578034 | | 2002 | 0.50493612746397 | | 2001 | 0.59923160950557 | | 2000 | 0.79054736728445 | | 1999 | 0.79283136578495 | | 1998 | 0.81208431951554 | | 1997 | 0.80146466869933 | | 1996 | 0.81734486733724 | | 1995 | 0.78188483368573 | | 1994 | 0.4712775202508 | | 1993 | 0.47749905097064 | | 1992 | 0.48194698872292 | | 1991 | 0.68278860620899 |
|