Year	Percent
1975	14.39
1978	20.17
1979	21.02
1980	21.01
1985	21.44
1986	31.09
1988	28.63
1989	26.97
1990	29.11
1991	28.67
1992	22.67
1994	25.86
1995	26.31
1996	24.91
1997	23.59
1998	24.57
1999	24.96
2000	24.22
2001	23.6
2002	24.22
2003	24.56
2004	23.68
2005	22.21
2006	22.98
2007	23.39
2008	23.46
2009	20.65
2010	21.35
2011	21.26
2012	20.98
2013	20.35
2014	20.89
2015	22.18
2016	21.1
2017	21.89