Year	Percent
1993	15.2
2003	15.8
2004	16.4
2005	16.3
2006	16.3
2007	16.8
2008	16.6
2009	16.9
2010	17
2011	16.6
2012	16.5
2013	15.9
2014	16.1
2015	16.4