Year	Percent
1970	24.59179
1971	21.27325
1972	20.85396
1973	23.44835
1974	32.62766
1975	29.72362
1976	29.2442
1977	27.70792
1978	25.78327
1979	30.40008
1980	30.01084
1981	31.26981
1982	30.47927
1983	29.37482
1984	34.0143
1985	31.0974
1986	26.13325
1987	23.90627
1988	22.05641
1989	25.48268
1990	25.83271
1991	25.46785
1992	28.05169
1993	26.98792
1994	28.11805
1995	27.52117
1996	26.76729
1997	26.92675
1998	28.27843
1999	30.45068
2000	32.77174
2001	31.80278
2002	29.80892
2003	28.07504
2004	29.25633
2005	29.73394
2006	29.97583
2007	29.12505
2008	32.29405
2009	26.41943
2010	27.96534
2011	28.81622
2012	28.16592
2013	27.22044
2014	27.15264
2015	26.81544
2016	25.50512