Year	Percent
1971	1.053
1972	2.372
1973	7.939
1974	11.07
1975	3.03
1976	2.049
1977	0.4757
1978	0.4404
1979	1.251
1980	1.959
1981	0.235
1982	0.2046
1983	0.2338
1984	1.854
1985	2.756
1986	4.128
1987	4.965
1988	6.61
1989	8.002
1990	5.677
1991	4.557
1992	4.322
1993	3.49
1994	2.53
1995	5.382
1996	6.206
1997	8.392
1998	8.711
1999	13.42
2000	14.64
2001	17.78
2002	17.76
2003	15.67
2004	13.37
2005	16.56
2006	19.43
2007	15.93