Year	Percent
1977	60.61608
1978	62.57452
1979	62.70881
1980	59.15627
1981	63.71184
1982	64.86259
1983	65.97153
1984	66.55135
1985	68.42586
1986	64.51868
1987	62.86336
1988	60.28976
1989	61.32275
1990	60.74409
1991	65.74917
1992	65.39126
1993	65.82881
1994	68.50655
1995	65.76616
1996	65.90304
1997	66.2446
1998	65.54438
1999	64.51333
2000	62.9851
2001	59.53609
2002	60.5315
2003	62.74113
2004	64.06825
2005	63.99776
2006	62.43071
2007	63.66904
2008	63.59614
2009	63.59854
2010	62.37017
2011	61.17989
2012	63.49896
2013	63.30217
2014	61.08909
2015	60.72315
2016	61.46781
2017	60.85599