2017 30.2238095238095
2016 30.9928961748634
2015 30.2550684931507
2014 29.6701369863014
2013 29.8293150684932
2012 29.7734972677596
2011 29.9641095890411
2010 30.652602739726
2009 29.9963636363636
2008 NA
2007 28.6205882352941
2006 30.2089108910891
2005 29.8732638888889
2004 29.1657060518732
2003 29.385342019544
2002 30.0026819923372
2001 30.1831325301205