Year	Percent
1971	4.75
1972	33.23
1973	19.66
1974	23.66
1975	26.26
1976	30.23
1977	10.56
1978	11.58
1979	11.27
1980	19.6
1981	23.71
1982	24.64
1983	20.72
1984	48.79
1985	50.25
1986	45.28
1987	41.42
1988	38.76
1989	33.57
1990	46.93
1991	39.24
1992	23.18
1993	38.94
1994	21.38
1995	29.1
1996	29.43
1997	27.97
1998	28.32
1999	27.47
2000	23.2
2001	14.43
2002	11.17
2003	10.28
2004	9.742
2005	8.053
2006	12.5
2007	12.09