Year	Percent
1973	33.94
1974	22.24
1975	33.99
1976	34.79
1977	28.26
1978	35.46
1979	27.42
1980	30.55
1981	37.3
1982	33.87
1983	20.05
1984	22.67
1985	31.69
1986	41.73
1987	20
1988	18.17
1990	59.7
1991	13.8
1992	24.08
1993	22.63
1994	20.56
1995	20.57
1998	10.85
1999	9.705
2000	8.731
2001	7.894
2002	7.409
2003	6.924
2004	8.25
2005	9.188
2006	10.01
2007	7.83