Year	Percent
1970	37.33254
1971	43.65486
1972	36.92589
1973	46.32845
1974	61.03972
1975	52.32871
1976	57.36983
1977	56.19815
1978	56.67807
1979	62.45344
1980	63.48735
1981	31.61921
1982	26.35139
1983	24.62087
1984	25.6637
1985	25.14489
1986	16.5015
1987	23.22216
1988	19.68743
1989	21.96502
1990	7.69832
1991	1.29041
1992	0.58241
1993	0.07555
1994	0.03557
1995	0.00538
1996	0.00916
1997	63.84701
1998	77.89899
1999	77.63488
2000	75.70377
2001	65.27339
2002	70.57005
2003	77.39272
2004	56.27091
2005	54.34787
2006	51.03194
2007	45.89984
2008	50.32831
2009	39.40011
2010	39.41683
2011	44.41752
2012	44.44873
2013	39.67639
2014	41.33845
2015	34.91884
2016	32.52166
2017	37.63154