Year	Percent
1986	29.83
1987	28.77
1989	26
1990	27.26
1991	24.51
1992	23.6
1993	24.43
1994	26.23
1996	21.53
1997	20.8
1998	20.2
1999	18.7
2000	18.85
2001	17.9
2002	14.41
2003	13.34
2004	14.4
2005	14.07
2006	14.85
2007	16.29
2008	16.44
2009	16.44
2010	16.85
2011	16.48
2012	17.03
2013	17.02
2014	16.37
2015	16.57
2016	16.22
2017	15.65