Year	Percent
1987	18.5
1988	17.3
1989	19.8
1990	20.41
1991	22.6
1992	24.67
1993	21.24
1995	32.19
1996	22.95
1997	21.23
1998	24.41
1999	13.32
2000	13.03
2001	12.51
2002	12.54
2003	12.97
2004	11.35
2005	11.55
2006	9.67
2007	9.43
2008	9.78
2009	9.28
2010	9.48
2011	10.22
2012	9.94
2013	9.57
2014	10.28
2015	10.39
2016	10.66