Year	Percent
1981	21.4
1982	21.8
1983	27.7
1984	26.9
1985	23.1
1986	10.5
1987	17.8
1988	20.1
1989	18.3
1990	21.6
1992	20.9
1993	19.9
1995	13
1996	14.2
1997	14
1998	12.7
1999	13.4
2001	11.6
2002	10.3
2003	11.1
2004	9.7
2005	8.6
2006	7.2
2007	6.8
2008	5.6
2009	5.4
2011	4.7
2012	3.8
2013	3.8
2014	2.8
2015	3.4