Year	Percent
1970	0.24582
1971	0.20901
1972	0.27285
1973	0.35376
1974	0.2732
1975	0.3708
1976	0.44
1977	0.24436
1978	0.37521
1979	0.32365
1980	0.44135
1981	0.73895
1982	0.48706
1983	0.30601
1984	0.39932
1985	0.40546
1986	0.70038
1987	0.98594
1988	1.4228
1989	1.90181
1990	2.74378
1991	1.88546
1992	2.23116
1993	1.55763
1994	1.75312
1995	0.98813
1996	1.89086
1997	2.44255
1998	3.04044
1999	8.40319
2000	12.74115
2001	6.3457
2002	3.54336
2003	2.8555
2004	2.8865
2005	5.4122
2006	5.62248
2007	4.97683
2008	4.65853
2009	3.29425
2010	2.74667
2011	2.25275
2012	1.93873
2013	0.62662
2014	1.86114
2015	2.1002
2016	2.97226
2017	2.20812