Year	Percent
1971	84.53
1972	83.66
1973	11.04
1974	11.37
1975	15.92
1976	18.91
1977	26.88
1978	21.82
1979	20.26
1980	19.79
1981	6.781
1982	4.478
1983	15.52
1984	36.97
1985	37.31
1986	34.13
1987	27.52
1988	24.49
1989	29.93
1990	22.13
1991	17.64
1992	18.52
1993	17.72
1994	17.13
1995	21.77
1996	13.63
1997	14.69
1998	20.38
1999	20.83
2000	19.68
2001	19.19
2002	21.63
2003	20.41
2004	25.64
2005	18.91
2006	20.63
2007	25.29