Year	Percent
1967	44.97
1968	38.67
1969	24.55
1970	38.84
1971	6.56
1972	9.343
1973	39.06
1974	38.3
1975	37.04
1976	40.3
1977	45.54
1978	43.51
1979	32.74
1980	29.81
1981	81.08
1982	82.52
1983	29.82
1984	22.01
1985	24.04
1986	21.99
1987	30.49
1988	22.35
1989	36.61
1990	15.51
1991	20.88
1992	18.62
1993	23.79
1994	25.65
1995	27.53
1996	26.37
1997	20.63
1998	22.72
1999	18.54
2000	16.76
2001	14.27
2002	12.23
2003	11.96
2004	11.79
2005	10.1
2006	10.36
2007	9.325