Year	Percent
1975	9.15
1977	7.8
1980	7.5
1983	9.1
1984	10.81
1985	10.66
1986	10.03
1987	8.24
1991	7.58
1992	6.69
1993	5.3
1994	5.28
1995	6.75
1996	9.44
1997	9.82
1998	12.52
1999	17.23
2000	16.94
2001	12.021
2002	12.565
2003	11.006
2004	10.708
2005	9.097
2007	8.739
2008	8.872
2009	9.367
2010	8.6407
2011	7.9127
2012	7.5481
2013	7.0747
2014	6.7156
2015	6.364
2016	6.7813
2017	6.8659