Year	Percent
1975	22.16422
1976	37.63685
1977	22.37668
1978	16.81336
1979	32.92288
1980	17.60942
1981	22.56805
1982	18.62643
1983	15.21077
1984	20.18769
1985	25.35891
1986	22.33206
1987	27.2534
1988	27.83303
1989	21.21431
1990	30.70653
1991	20.85151
1992	20.28116
1993	30.17323
1994	24.72953
1995	23.12142
1996	22.71164
1997	24.68826
1998	27.83853
2006	5.84759
2007	7.45393
2008	3.08117
2009	4.74509
2010	4.88908
2011	3.89736
2012	5.02273
2013	5.58224
2014	9.86877
2015	12.13109
2016	13.16346