Year	Percent
1997	43.7
1998	57.9
1999	70
2000	68.8
2001	60
2002	44.4
2003	32.2
2004	32.8
2005	40.4
2006	12.9
2007	7.8
2008	9.2
2009	8.2
2010	6.1
2011	4.3
2012	3.4
2013	2.2
2014	1.1
2015	1.4
2016	1.3