| Year | Value | | 2017 | 61.6 | | 2016 | 60 | | 2015 | 58 | | 2014 | 57 | | 2013 | 54.9 | | 2012 | 49.05008307 | | 2011 | 40.22 | | 2010 | 37.37 | | 2009 | 32.7 | | 2008 | 25.88 | | 2007 | 20.83 | | 2006 | 15.22471148 | | 2005 | 12.55299791 | | 2004 | 8.404469592 | | 2003 | 7.499963465 | | 2002 | 4.910446327 | | 2001 | 4.636000948 | | 2000 | 3.359597465 | | 1999 | 2.839825767 | | 1998 | 1.383990391 | | 1997 | 0.390959318 | | 1996 | 0.24826058 | | 1995 | 0.122214848 | | 1994 | 0.055486978 | | 1993 | 0.041587233 | | 1992 | 0.012082134 |
|