Year	Percent
1967	54.44
1968	48.63
1969	52.87
1970	29.9
1971	19.88
1972	31.8
1973	43.92
1974	33.69
1975	50.58
1976	30.16
1977	44.22
1978	38.33
1979	36.78
1980	43.61
1981	55.76
1982	39.1
1983	35.06
1984	35.07
1985	33.39
1986	29.94
1987	29.61
1988	29.38
1989	40.13
1990	22.97
1991	17.55
1992	15
1993	24.35
1994	16.6
1995	13.33
1996	11.62
1997	9.092
1998	8.782
1999	9.992
2000	11.68
2001	9.654
2002	7.853
2003	7.232
2004	9.799
2005	8.219
2006	7.821
2007	6.901