Year	Percent
1971	33.7
1972	38.57
1973	17.97
1974	25.28
1975	8.415
1976	5.137
1977	8.449
1978	3.281
1979	3.351
1980	0.9856
1981	7.22
1982	9.669
1983	9.353
1984	7.136
1985	16.22
1986	10.06
1987	18.88
1988	12.29
1989	28.11
1990	25.09
1991	14.35
1992	11.19
1993	9.291
1994	21.67
1995	17.33
1996	13.98
1997	25.19
1998	15.66
1999	19.1
2000	18.61
2001	20.25
2002	25.99
2003	25.76
2004	15.84
2005	15.83
2006	19.4
2007	11.03