Year	Percent
1977	62.66352
1978	62.02337
1979	59.74728
1980	60.55665
1981	62.42032
1982	63.59455
1983	64.5921
1984	64.44287
1985	64.21969
1986	61.26606
1987	63.90257
1988	60.00624
1989	61.1305
1990	64.54099
1991	64.70507
1992	63.06768
1993	65.51384
1994	67.64437
1995	67.83615
1996	68.15375
1997	70.21906
1998	66.93871
1999	67.47547
2000	68.04787
2001	70.77405
2002	69.62149
2003	70.36877
2004	68.74569
2005	67.96671
2006	61.61179
2007	73.15966
2008	71.41638
2009	71.26383
2010	74.98311
2011	75.47629
2012	75.78879
2013	73.7586
2014	74.55948
2015	74.41406
2016	73.55284
2017	74.21122