Year	Percent
1971	17.44379
1972	10.11462
1973	12.07822
1974	19.56273
1975	16.54896
1976	9.4108
1977	0.7424
1978	1.63409
1979	1.54338
1980	7.59112
1981	17.95198
1982	31.74419
1983	20.95373
1984	22.11532
1985	16.30518
1986	6.75431
1987	0.69106
1988	2.55203
1989	1.17829
1990	6.99763
1991	7.86214
1992	1.96072
1993	0.1493
1994	4.31749
1995	3.50973
1996	5.87887
1997	6.68964
1998	0.43138
1999	0.54128
2000	4.93906
2001	0.38993
2002	4.12521
2003	5.35541
2004	10.99709
2005	17.32527
2006	26.68344
2007	25.4733
2008	89.86545
2009	85.75054
2010	68.77874
2011	77.0913
2012	81.94553
2013	69.47571
2014	58.22411
2015	36.83958
2016	15.54807