Year	Percent
1968	100
1969	69.96
1970	40.61
1971	75.34
1972	57.66
1973	78.73
1974	82.57
1975	66.3
1976	91.41
1977	39.86
1978	54.12
1979	45.06
1980	62.88
1981	38.64
1982	18.26
1983	13.26
1984	5.394
1985	14.84
1986	7.958
1987	7.442
1988	13.22
1989	24.92
1990	12.17
1991	13.65
1992	5.968
1993	30.37
1994	14.64
1995	23.09
1996	12.5
1997	9.524
1998	11.96
1999	3.573
2000	8.084
2001	6.627
2002	5.803
2003	7.419
2004	7.298
2005	9.788
2006	6.564
2007	5.996