2017 NA
2016 NA
2015 NA
2014 NA
2013 NA
2012 NA
2011 NA
2010 NA
2009 NA
2008 23.3081967213115
2007 24.5323287671233
2006 24.5493150684932
2005 24.2539726027397
2004 24.101912568306
2003 24.4087671232877
2002 24.3317808219178
2001 24.1504109589041