Year	Percent
1970	4.53464
1971	4.89742
1972	3.46774
1973	4.60569
1974	6.32358
1975	6.73919
1976	8.82148
1977	14.78699
1978	17.93847
1979	16.96308
1980	17.16757
1981	18.58168
1982	20.17167
1983	25.01054
1984	28.17757
1985	33.04242
1986	31.4982
1987	35.04835
1988	32.47258
1989	27.54765
1990	26.94521
1991	30.9499
1992	46.58044
1993	48.26231
1994	60.34118
1995	53.77775
1996	50.18252
1997	53.34261
1998	52.20769
1999	53.53602
2000	55.25762
2001	54.07366
2002	48.78466
2003	41.769
2004	40.17808
2005	36.76122
2006	19.37091
2007	21.69493
2008	18.96587
2009	22.97415
2010	23.34522
2011	22.03977
2012	23.49885
2013	21.86739
2014	21.16207
2015	24.25193
2016	23.90544