Year	Percent
1971	6.412
1972	5.184
1973	5.106
1974	5.283
1975	7.017
1976	6.584
1977	6.764
1978	9.05
1979	9.727
1980	12.27
1981	12.82
1982	12.16
1983	11.3
1984	10.8
1985	11.3
1986	12.65
1987	9.719
1988	8.245
1989	10.06
1990	12.3
1991	11.67
1992	11.2
1993	13.78
1994	12.46
1995	12.63
1996	12.92
1997	8.313
1998	8.222
1999	8.268
2000	8.264
2001	8.271
2002	8.256
2003	8.248
2004	8.298
2005	8.309
2006	8.344
2007	8.304
2008	8.317
2009	8.305
2010	8.324