Year	Percent
1970	20.32487
1971	19.81347
1972	18.82428
1973	19.59903
1974	19.91021
1975	21.34991
1976	27.82028
1977	39.42653
1978	36.05405
1979	32.93917
1980	30.63778
1981	32.67626
1982	53.43421
1983	66.66371
1984	57.39248
1985	55.31406
1986	82.90893
1987	82.15988
1988	56.50965
1989	43.79473
1990	41.16926
1991	37.34554
1992	31.76561
1993	26.77025
1994	27.20455
1995	50.44855
1996	41.09457
1997	31.82043
1998	32.77377
1999	29.64453
2000	22.81647
2001	23.36116
2002	21.57794
2003	22.63852
2004	21.83734
2005	20.08143
2006	18.06616
2007	18.72776
2008	17.84361
2009	21.42612
2010	23.17146
2011	24.85555
2012	29.49215
2013	32.68068
2014	34.33437
2015	37.32185
2016	40.6776