Year	Percent
1971	14.26
1972	13.09
1973	12.62
1974	11.91
1975	12.03
1976	11.28
1977	10.64
1978	11.21
1979	10.57
1980	10.08
1981	11.72
1982	11.47
1983	12.52
1984	12.01
1985	12.95
1986	10.67
1987	10.47
1988	10.66
1989	11.38
1990	9.871
1991	8.268
1992	9.757
1993	8.964
1994	8.525
1995	8.397
1996	8.434
1997	8.144
1998	8.02
1999	10.84
2000	10.59
2001	10.47
2002	10.42
2003	10.25
2004	10.82
2005	10.91
2006	9.689
2007	12.25
2008	11.8
2009	11.69
2010	10.35