Year	Percent
1970	20.18944
1971	22.99473
1972	21.48229
1973	24.60777
1974	31.574
1975	42.57353
1976	35.91265
1977	40.83336
1978	31.64885
1979	31.16359
1980	31.56233
1981	62.29278
1982	66.43806
1983	32.93162
1984	29.66414
1985	29.81654
1986	26.43735
1987	26.12727
1988	22.81214
1989	22.87007
1990	7.42796
1991	2.50073
1992	1.33874
1993	0.46915
1994	0.06402
1995	0.01562
1996	0.01773
1997	42.34116
1998	54.34417
1999	60.67972
2000	49.63282
2001	61.50686
2002	49.192
2003	76.84181
2004	63.96307
2005	61.39467
2006	38.61858
2007	28.19301
2008	30.72724
2009	39.28727
2010	34.08065
2011	27.75381
2012	29.10025
2013	36.01133
2014	36.9489
2015	40.92399
2016	40.89933
2017	36.31822