Year	Percent
1993	17
1996	17.5
2004	17.7
2005	17.8
2006	17.8
2007	17.7
2008	17.6
2009	17.7
2010	17.7
2011	17.9
2012	17.9
2013	17.8
2014	17.8
2015	17.8