2017 NA
2016 NA
2015 NA
2014 NA
2013 NA
2012 NA
2011 NA
2010 NA
2009 NA
2008 30.1540983606557
2007 31.3824657534247
2006 31.1309589041096
2005 31.3309589041096
2004 29.918306010929
2003 30.7147945205479
2002 30.9887671232877
2001 30.5841095890411