Year	Percent
1971	12.8697
1972	19.81534
1973	24.79339
1974	20.70361
1975	33.2781
1976	30.67963
1977	25.04225
1978	27.93326
1979	20.85433
1980	19.87984
1981	20.95123
1982	22.22137
1983	22.87916
1984	22.52406
1985	20.74862
1986	21.15544
1987	17.60309
1988	18.2664
1989	16.66667
1990	16.52126
1991	14.75188
1992	16.24546
1993	15.36764
1994	15.6886
1995	14.62353
1996	12.54277
1997	12.47721
1998	12.61777
1999	11.50678
2000	10.81231
2001	12.50838
2002	12.42677
2003	12.18853
2004	12.05435
2005	11.81698
2006	10.82917
2007	10.27939
2008	7.58003
2009	9.27958
2010	8.34767
2011	9.81433
2012	16.15662
2013	14.80698
2014	13.51448
2015	14.3842
2016	15.95615
2017	12.07272