Year	Percent
1971	0.632
1972	1.282
1973	2.317
1974	3.034
1975	3.216
1976	3.566
1977	4.689
1978	5.098
1979	5.507
1980	6.308
1981	7.747
1982	9.198
1983	11.41
1984	9.102
1985	9.567
1986	14.44
1987	14.55
1988	14.18
1989	14.13
1990	13.51
1991	9.115
1992	10.65
1993	12.6
1994	16.64
1995	13.26
1996	12.97
1997	13.57
1998	15.5
1999	13.59
2000	12.51
2001	11.92
2002	11.96
2003	11.85
2004	13.59
2005	10.76
2006	11.14
2007	11.4
2008	16.17
2009	16.85
2010	11.67