2017 NA
2016 NA
2015 NA
2014 NA
2013 NA
2012 NA
2011 NA
2010 NA
2009 29.8721763085399
2008 29.6083582089552
2007 30.0206611570248
2006 30.5581267217631
2005 31.0821917808219
2004 30.7505263157895
2003 31.2550684931507
2002 30.9197260273973
2001 30.8347945205479