Year	Percent
1992	8.9
1996	16.5
1999	20.1
2000	16.4
2001	19.7
2002	14.3
2003	12
2004	10.9
2005	9.7
2008	10.4
2009	9
2010	7.8
2011	6.4
2012	6.3
2013	5.7
2014	5
2015	4.5
2016	4.5