Year	Percent
1970	6.5
1971	7
1972	6.8
1973	5.8
1974	5.6
1975	6.2
1976	6.4178
1977	7.359
1978	7.6368
1979	6.7696
1980	7.0104
1981	7.1636
1982	11.2475
1983	12.3427
1984	11.37
1985	10.453
1986	9.4701
1987	8.5275
1988	7.4292
1989	7.373
1990	8.1629
1991	10.8227
1992	12.0131
1993	11.9491
1994	10.8856
1995	9.7976
1996	9.8941
1997	9.2518
1998	8.5234
1999	7.8275
2000	6.9425
2001	7.5282
2002	8.1297
2003	7.9359
2004	7.4759
2005	7.0147
2006	6.5215
2007	6.3802
2008	6.5686
2009	9.5385
2010	8.7931
2011	7.9625
2012	7.716
2013	7.5044
2014	7.3848
2015	7.4607
2016	7.6803
2017	6.7814