2017 27.7430136986301
2016 27.6707650273224
2015 27.6917808219178
2014 27.3578082191781
2013 27.512602739726
2012 27.5579234972678
2011 27.5405479452055
2010 28.101095890411
2009 27.6391780821918
2008 27.3096153846154
2007 27.6899721448468
2006 27.6877437325905
2005 27.7765193370166
2004 27.4057534246575
2003 27.3137931034483
2002 NA
2001 NA