Year	Percent
1970	9.6
1971	8.6
1972	7.6
1973	11.4
1974	10.2
1981	9
1982	15.5
1984	17.56
1986	13.9
1987	12.6
1990	10.92
1991	11.57
1992	11.84
1993	10.9
1994	11.88
1995	12.91
1998	12.72
1999	14.59
2000	16.76
2001	19.43
2002	21.13
2003	20.41
2004	16.4879
2005	15.1143
2006	14.1116
2007	12.6225
2008	10.8156
2009	10.3667
2010	9.3958
2011	8.0691
2012	8.2565
2013	8.2022
2014	8.344
2015	8.8459
2016	9.4442
2017	9.4721