Year	Percent
1971	5.12493
1972	8.56858
1973	8.29686
1974	2.49648
1975	2.7946
1976	4.1549
1977	8.12048
1978	2.28563
1979	1.61847
1980	0.38726
1981	0.3269
1982	0.07861
1983	0.28544
1984	0.37504
1985	0.1759
1986	1.24733
1987	0.57781
1988	1.29341
1989	0.92689
1990	2.99811
1991	3.11007
1992	4.9103
1993	3.00532
1994	4.59589
1995	4.06083
1996	6.37184
1997	9.06376
1998	8.27261
1999	10.08454
2000	13.84383
2001	18.08735
2002	21.76008
2003	27.89986
2004	26.61077
2005	24.39007
2006	55.15764
2007	57.3893
2008	47.63671
2009	45.15615
2010	43.90655
2011	37.21367
2012	34.96892
2013	35.56607
2014	30.59011
2015	26.269