Year	Percent
1987	35.3
1994	35.8
2002	31.8
2003	36.5
2004	27.3
2005	25.7
2006	23.2
2007	19.8
2008	16.9
2009	16.7
2010	15.9
2011	13.6
2012	13
2013	11.4
2014	10.5
2015	11.5
2016	9.9