Year	Percent
1983	14.89
1984	15.04
1985	14.6
1986	15.29
1987	14.61
1988	14.3
1989	14.18
1990	12.83
1991	11.6
1992	12.03
1993	12.05
1994	12.29
1995	12.34
1996	12
1997	11.92
1998	11.26
1999	10.04
2000	9.62
2001	8.33
2002	7.82
2003	7.86
2004	6.28
2005	6.32
2006	6.54
2007	6.36
2008	5.88
2009	5.84
2010	5.67
2011	5.47
2012	5.02
2013	4.89
2014	4.7
2015	4.37
2016	3.91
2017	3.93