2017 30.6043835616438
2016 30.7142076502732
2015 30.5230136986301
2014 29.9556164383562
2013 29.8358904109589
2012 29.3071038251366
2011 29.5909589041096
2010 30.3317808219178
2009 29.421095890411
2008 29.4245901639344
2007 29.6561643835616
2006 29.8060273972603
2005 30.2898630136986
2004 29.6385245901639
2003 30.3657534246575
2002 29.8523287671233
2001 30.3016438356164