2017 29.9802739726027
2016 30.25
2015 29.7183561643836
2014 29.1356164383562
2013 29.6090410958904
2012 29.5724043715847
2011 29.7887671232877
2010 30.3276712328767
2009 29.4671232876712
2008 28.9950819672131
2007 29.3849315068493
2006 29.5734246575342
2005 29.8204402515723
2004 29.1494464944649
2003 29.5319327731092
2002 28.8053497942387
2001 30.0217741935484