2017 28.348253968254
2016 NA
2015 27.2741935483871
2014 28.5797142857143
2013 27.9994594594595
2012 27.1161290322581
2011 29.0895890410959
2010 29.7767123287671
2009 28.8693150684932
2008 28.4480597014925
2007 28.9669491525424
2006 28.8727272727273
2005 29.14
2004 28.3683076923077
2003 28.1634920634921
2002 28.4786585365854
2001 28.4155619596542