Year	Percent
1970	0.11711
1971	0.0745
1972	0.10527
1973	0.1484
1974	0.215
1975	0.15158
1976	0.17309
1977	0.13903
1978	0.24824
1979	0.33053
1980	0.59144
1981	0.7845
1982	0.37292
1983	0.28778
1984	0.61277
1985	0.46035
1986	0.77163
1987	1.20058
1988	1.09918
1989	1.20632
1990	0.81093
1991	0.37544
1992	0.30294
1993	0.74694
1994	0.63116
1995	0.75417
1996	1.06812
1997	1.22658
1998	1.96971
1999	2.99611
2000	3.40373
2001	1.61433
2002	0.99718
2003	1.01737
2004	1.74047
2005	1.08712
2006	2.15405
2007	2.39413
2008	2.31742
2009	1.11718
2010	1.76445
2011	1.69802
2012	1.54962
2013	1.72621
2014	1.44516
2015	2.80942
2016	2.65488
2017	1.8299