2017 NA
2016 NA
2015 NA
2014 NA
2013 NA
2012 NA
2011 NA
2010 NA
2009 NA
2008 27.5738805970149
2007 27.0275362318841
2006 27.5727554179567
2005 27.7076712328767
2004 26.7947214076246
2003 28.2152631578947
2002 26.4348837209302
2001 26.8893150684932