2017 26.6351111111111
2016 27.2245901639344
2015 27.1349823321555
2014 26.7813411078717
2013 26.9441860465116
2012 26.9622950819672
2011 26.9300578034682
2010 27.3807799442897
2009 26.9234042553191
2008 NA
2007 25.9071428571429
2006 27.4038647342995
2005 26.8360424028269
2004 26.3746268656716
2003 26.6299319727891
2002 27.0246031746032
2001 27.3368098159509