2017 26.8041095890411
2016 26.9530054644809
2015 27.4126168224299
2014 NA
2013 NA
2012 NA
2011 26.7829411764706
2010 27.2709589041096
2009 26.6994318181818
2008 26.433698630137
2007 26.8772222222222
2006 26.8095100864553
2005 27.0345403899721
2004 27.0676595744681
2003 NA
2002 NA
2001 NA