Year	Percent
1977	63.39568
1978	60.19592
1979	59.93653
1980	62.84636
1981	60.59694
1982	59.98682
1983	61.54018
1984	59.25795
1985	57.61642
1986	56.39106
1987	57.15563
1988	54.04301
1989	56.10467
1990	56.82168
1991	58.75838
1992	57.6996
1993	60.13166
1994	62.45043
1995	60.51809
1996	61.59005
1997	62.20685
1998	61.62548
1999	62.65055
2000	63.17019
2001	64.53504
2002	65.26242
2003	65.40789
2004	65.47165
2005	66.09947
2006	64.89197
2007	66.39587
2008	63.13911
2009	62.67628
2010	63.20441
2011	64.21822
2012	64.88829
2013	64.73784
2014	64.54047
2015	63.67089
2016	63.09071
2017	62.26044