Year	Percent
1970	17.24313
1971	25.4569
1972	45.23744
1973	47.01806
1974	43.3262
1975	41.66455
1976	44.71679
1977	41.09026
1978	21.26405
1979	15.85847
1980	13.37457
1981	14.35527
1982	19.62385
1983	20.1416
1984	23.6892
1985	33.94463
1986	31.74737
1987	31.42581
1988	21.58003
1989	19.5171
1990	15.00575
1991	15.29232
1992	14.23725
1993	14.90852
1994	17.35798
1995	15.26454
1996	13.636
1997	11.78833
1998	10.83845
1999	9.77009
2000	8.32267
2001	7.47973
2002	10.36455
2003	7.56528
2004	6.44918
2005	5.06329
2006	3.89922
2007	4.16818
2008	4.39876
2009	16.38531
2010	14.76608
2011	15.38279
2012	17.08823
2013	16.36342
2014	15.99609
2015	15.72561
2016	14.04477