Year	Percent
1993	17.5
1995	17.3
1996	17.3
2004	15.9
2005	15.3
2006	16
2007	15.9
2008	16.1
2009	16.5
2010	17.1
2011	16.4
2012	16.5
2013	16.2
2014	16.3
2015	16.4