| Year | Value | | 2020 | 0.51824838954313 | | 2019 | 0.48671747997158 | | 2018 | 0.49367763508666 | | 2017 | 0.49179118546265 | | 2016 | 0.42256111808015 | | 2015 | 0.42049994970491 | | 2014 | 0.41817068723843 | | 2013 | 0.42337719521076 | | 2012 | 0.43431807718701 | | 2011 | 0.44014936908989 | | 2010 | 0.34990054077129 | | 2009 | 0.35768257459917 | | 2008 | 0.36181020883685 | | 2007 | 0.36613942589338 | | 2005 | 0.36700278004606 | | 2003 | 0.36640236842491 | | 2002 | 0.38471378256362 | | 2001 | 0.31445428424309 | | 2000 | 0.34950438336748 | | 1999 | 0.35269083513271 | | 1998 | 0.35739601265182 | | 1997 | 0.36193781506184 | | 1996 | 0.36756447693533 | | 1995 | 0.37274798094844 | | 1994 | 0.21002667338752 | | 1993 | 0.21423827581036 | | 1992 | 0.21799458065472 | | 1991 | 0.2219135158646 |
|