Year	Percent
1975	26.48984
1976	25.1198
1977	19.36187
1978	15.12199
1979	13.67268
1980	13.41609
1981	15.46282
1982	18.20368
1983	18.9584
1984	15.29166
1985	19.51281
1986	25.25339
1987	27.78983
1988	25.89671
1989	22.15573
1990	16.12586
1991	16.17326
1992	15.1473
1993	11.5711
1994	10.12378
1995	9.33928
1996	9.27281
1997	9.24816
1998	9.86664
1999	13.27782
2000	12.12288
2001	11.84565
2002	11.75208
2003	9.09939
2004	10.45799
2005	5.5415
2006	10.83463
2007	8.84068
2008	12.04151
2009	15.64
2010	12.32871
2011	9.32001
2012	14.79011
2013	13.4646
2014	37.62957
2015	19.98881
2016	17.93497