Year	Percent
1971	16.79
1972	15.32
1973	16.1
1974	13.43
1975	15.48
1976	13
1977	12.9
1978	12.3
1979	14.99
1980	14.74
1981	9.409
1982	8.937
1983	10.04
1984	9.826
1985	10.99
1986	10.54
1987	10.61
1988	10.52
1989	11.55
1990	12.71
1991	13.13
1992	12.09
1993	12.83
1994	13.44
1995	14.46
1996	15.51
1997	15.41
1998	12.47
1999	10.34
2000	12.52
2001	12.76
2002	14.25
2003	15.23
2004	16.15
2005	16.8
2006	16.02
2007	15.76
2008	16.01
2009	14.93
2010	16.04