Year	Percent
1970	39.42494
1971	42.58706
1972	39.98926
1973	53.42023
1974	47.56267
1975	41.13478
1976	38.06448
1977	42.98694
1978	49.99965
1979	62.5298
1980	59.64547
1981	41.36185
1982	37.45689
1983	39.12518
1984	46.93856
1985	50.04996
1986	53.75311
1987	50.04707
1988	49.86072
1989	38.94099
1990	43.03949
1991	37.33221
1992	45.07022
1993	37.57164
1994	83.6092
1995	61.81907
1996	42.52648
1997	51.01452
1998	43.5925
1999	45.4451
2000	32.68734
2001	31.86514
2002	27.17369
2003	27.28867
2004	29.93734
2005	33.27768
2006	33.96191
2007	39.50314
2008	37.81023
2009	39.16467
2010	37.97779
2011	43.85439
2012	31.60135
2013	32.0906
2014	36.09332
2015	43.82581
2016	42.05044
2017	44.03381