Year	Percent
1970	30.02684
1971	26.64201
1972	22.88992
1973	20.27516
1974	24.88436
1975	21.56204
1976	25.228
1977	23.82015
1978	21.51483
1979	23.37165
1980	22.57687
1981	24.83643
1982	28.93152
1983	27.48765
1984	26.51173
1985	25.78056
1986	23.39095
1987	25.23853
1988	26.40662
1989	27.15323
1990	30.62668
1991	28.96002
1992	25.27804
1993	27.37688
1994	28.09763
1995	31.08165
1996	27.57539
1997	24.3674
1998	22.22222
1999	21.56658
2000	26.59901
2001	18.53956
2002	15.70337
2003	19.06689
2004	19.10339
2005	21.34536
2006	21.27885
2007	20.97091
2008	21.68649
2009	20.76532
2010	23.61088
2011	19.42808
2012	17.97637
2013	19.02594
2014	17.67519
2015	23.91117
2016	23.14189