2017 29.7761643835616
2016 30.0508196721311
2015 29.9320547945205
2014 29.7257534246575
2013 29.8632876712329
2012 29.9527322404372
2011 29.8427397260274
2010 30.3945205479452
2009 29.5558904109589
2008 29.4459016393443
2007 29.8344729344729
2006 29.8632876712329
2005 30.0660273972603
2004 29.547619047619
2003 29.8578082191781
2002 29.603661971831
2001 29.7359331476323