Year	Percent
1975	3.24522
1976	3.49172
1977	2.89052
1978	28.12056
1979	2.81357
1980	2.38367
1981	2.22939
1982	2.1181
1983	2.11887
1984	2.18531
1985	6.63175
1986	6.72115
1987	6.39348
1988	7.5224
1989	18.22802
1990	15.81113
1991	13.94287
1992	10.124
1993	13.782
1994	14.1596
1995	12.70227
1996	13.45183
1997	17.30344
1998	1.19132
1999	15.20493
2000	15.211
2001	12.77218
2002	15.73647
2003	21.59853
2004	29.17083
2005	39.95623
2006	57.37236
2007	60.8319
2008	17.72942
2009	28.50674
2010	32.15981
2011	19.77859
2012	25.89894
2013	27.36107
2014	21.90394
2015	25.14733
2016	30.95618
2017	36.1612