2017 NA
2016 NA
2015 NA
2014 NA
2013 NA
2012 NA
2011 NA
2010 NA
2009 NA
2008 22.3789617486339
2007 22.6454794520548
2006 22.7304109589041
2005 22.8457534246575
2004 22.7489071038251
2003 22.7895890410959
2002 22.96
2001 22.8745205479452