Year	Percent
1971	24.67
1972	42.34
1973	13.46
1974	2.523
1975	15.94
1976	4.851
1977	19.1
1978	16.97
1979	45.06
1980	17.64
1981	7.565
1982	0.697
1983	15.39
1984	31.79
1985	44.36
1986	29.75
1987	32.12
1988	16.36
1989	12.23
1990	31.86
1991	31.07
1992	31.57
1993	24.02
1994	28.61
1995	30.52
1996	44.99
1997	35.41
1998	48.95
1999	36.29
2000	29.39
2001	42.67
2002	33.24
2003	39.51
2004	40.78
2005	38.86
2006	39.49
2007	40.73