Year	Percent
1987	15.8
1988	17.16
1989	17.33
1990	15.71
1991	14.62
1993	16.8
1995	13.83
1996	13.19
1998	11.08
1999	10.01
2000	9.18
2002	8.02
2005	5.75
2006	4.68
2007	4.14
2008	3.43
2009	4.26
2010	3.12
2011	2.75
2012	3.15
2013	2.37
2014	2.25
2015	2.16
2016	2.81