Year	Percent
1977	68.91808
1978	68.40282
1979	72.87551
1980	70.82867
1981	67.89793
1982	67.80361
1983	69.2744
1984	69.12593
1985	69.92483
1986	68.4448
1987	67.96442
1988	65.87757
1989	69.62946
1990	69.8689
1991	72.39796
1992	72.59746
1993	72.86159
1994	75.27262
1995	75.86886
1996	75.61618
1997	75.13266
1998	76.10632
1999	76.0688
2000	61.69734
2001	62.73944
2002	62.4671
2003	62.29773
2004	60.80639
2005	59.86187
2006	60.87418
2007	59.04485
2008	58.48247
2009	59.41386
2010	60.29376
2011	59.03345
2012	60.15161
2013	59.41751
2014	59.29965
2015	59.55242
2016	57.68329
2017	58.00926