Year	Percent
1986	25.0006
1987	27.9218
1988	27.9958
1989	25.2695
1990	24.1748
1991	23.2062
1992	25.2305
1993	28.7385
1994	31.5898
1995	30.5261
1996	29.5265
1997	27.9835
1998	26.609
1999	22.8054
2000	20.3258
2001	15.0379
2002	16.0425
2003	15.6832
2004	15.0345
2005	11.986
2006	11.3437
2007	10.6975
2008	12.8389
2009	18.1267
2010	20.2247
2011	21.8119
2012	25.0337
2013	26.6715
2014	25.4253
2015	23.5483
2016	21.3797
2017	19.0273