Year	Percent
1970	0.43893
1971	1.03742
1972	1.20174
1973	2.0681
1974	2.26232
1975	2.15866
1976	3.40003
1977	7.24125
1978	6.98701
1979	7.87011
1980	10.44416
1981	12.18498
1982	14.65517
1983	18.39074
1984	17.93779
1985	22.5136
1986	26.09466
1987	33.35126
1988	33.45279
1989	38.39116
1990	44.6918
1991	44.87297
1992	52.66659
1993	54.61758
1994	56.89101
1995	54.68986
1996	52.94574
1997	48.99155
1998	54.90693
1999	60.06892
2000	52.19027
2001	45.49493
2002	49.66764
2003	50.8802
2004	46.4669
2005	39.14126
2006	37.3614
2007	34.65636
2008	29.18943
2009	29.04739
2010	23.49609
2011	20.12962
2012	22.21339
2013	20.66602
2014	20.4855
2015	19.11027
2016	19.72085