Year	Percent
1984	30.21
1986	31.25
1987	34.5
1988	33.5
1989	34.09
1990	33.03
1991	32.98
1992	29.55
1993	29.34
1994	27.96
1995	26.65
1998	24.73
1999	25.19
2000	24.66
2001	23.82
2002	22.42
2003	21.5
2004	21.6
2005	21.92
2006	21.16
2007	21.68
2008	21.55
2009	20.96
2010	21.41
2011	20.78
2012	21.13
2013	21.58
2014	21.01
2015	20.46
2016	20.05
2017	19.73