Year	Percent
1980	5.5
1986	4.9
1987	8.3
1991	14.2
1992	14.9
1993	15
1994	15.7
1995	20.5
1996	22.3
1997	21.3
1998	23.2
1999	24.2
2000	26.3
2001	31
2002	44.2
2003	30.3
2004	25.9
2005	21.7
2006	17.5
2007	16.6
2008	14.9
2009	13.8
2010	11.1
2011	8.9
2012	8.5
2013	8.3
2014	9.1
2016	7.8