2017 NA
2016 NA
2015 NA
2014 NA
2013 NA
2012 NA
2011 NA
2010 NA
2009 22.0958904109589
2008 22.733606557377
2007 22.6607438016529
2006 23.1224376731302
2005 23.2931506849315
2004 22.9540983606557
2003 22.9353424657534
2002 21.7878378378378
2001 20.8443113772455