Year	Percent
1983	29.09
1984	29.06
1985	29.25
1986	29.27
1987	29.09
1988	29.28
1989	29.01
1990	22.86
1991	22.27
1992	20.27
1993	19.16
1994	18.77
1995	17.77
1996	15.12
1997	14
1998	11.12
1999	11.17
2000	10.88
2001	10.82
2002	11.53
2003	12.9
2004	11.91
2005	12.08
2006	12.35
2007	12.63
2008	12.13
2009	12.67
2010	13.72
2011	14.07
2012	14.29
2013	14.38
2014	14.3
2015	14.06
2016	14.33
2017	14.37