Year	Percent
1977	75.0553
1978	75.61691
1979	75.10734
1980	73.55597
1981	73.13745
1982	75.69758
1983	76.52254
1984	76.79312
1985	75.81475
1986	72.35998
1987	71.85339
1988	71.74205
1989	71.51494
1990	72.49296
1991	72.31401
1992	73.23858
1993	74.21682
1994	74.2127
1995	73.67479
1996	73.67429
1997	74.02354
1998	74.43422
1999	74.15312
2000	76.31446
2001	75.85453
2002	74.99441
2003	74.54421
2004	73.16337
2005	72.59407
2006	68.25972
2007	67.60772
2008	67.2195
2009	68.4882
2010	70.99451
2011	72.39035
2012	72.00084
2013	71.33837
2014	71.23371
2015	70.51097
2016	69.11122
2017	69.21995