Year	Percent
1971	4.488
1972	3.841
1973	5.391
1974	2.616
1975	0.9823
1976	1.465
1977	2.898
1978	2.388
1979	3.047
1980	3.369
1981	2.91
1982	4.882
1983	3.405
1984	4.011
1985	5.015
1986	5.273
1987	3.586
1988	3.102
1989	3.032
1990	4.378
1991	3.876
1992	3.268
1993	4.482
1994	4.068
1995	4.53
1996	3.334
1997	3.351
1998	4.986
1999	3.917
2000	7.035
2001	7.218
2002	8.826
2003	9.819
2004	8.993
2005	10.93
2006	11.92
2007	16.46