Year	Percent
1997	16.1
1998	27.6
1999	39.1
2000	35.9
2001	27.6
2002	16.6
2003	7.6
2004	8.7
2005	14
2006	2.4
2007	1.1
2008	1.3
2009	1
2010	0.5
2011	0.3
2012	0.3
2013	0.1
2014	0
2015	0
2016	0.2