Year	Percent
1971	100
1972	100
1973	13.69
1974	18.98
1975	5.599
1976	15.35
1977	3.827
1978	13.84
1979	8.244
1980	9.502
1981	13.52
1982	0.5299
1983	5.761
1984	10.23
1985	3.696
1986	3.318
1987	3.715
1988	4.6
1989	1.485
1990	1.933
1991	13.52
1992	10.71
1993	13.01
1994	4.193
1995	7.937
1996	4.303
1997	11.42
1998	7.581
1999	1.579
2000	10.69
2001	4.855
2002	13.17
2003	5.523
2004	9.206
2005	9.6
2006	2.129
2007	5.607