2017 23.0441095890411
2016 23.3235474006116
2015 NA
2014 NA
2013 22.864406779661
2012 23.8383886255924
2011 22.9
2010 23.2188612099644
2009 22.539886039886
2008 22.7328413284133
2007 22.7571428571429
2006 22.8152905198777
2005 23.3213483146067
2004 22.7381215469613
2003 22.8153203342618
2002 22.8498233215548
2001 NA