Year	Percent
1960	66.27822
1961	65.84709
1962	65.13586
1963	64.41506
1964	63.91595
1965	63.94688
1966	65.2779
1967	66.94824
1968	69.08916
1969	71.79542
1970	73.98559
1971	72.03405
1972	70.53805
1973	69.3015
1974	68.16157
1975	67.13017
1976	66.54159
1977	65.97573
1978	65.49832
1979	65.16389
1980	64.94071
1981	64.67248
1982	64.66466
1983	64.74829
1984	64.73074
1985	64.50373
1986	63.78638
1987	62.94162
1988	62.62447
1989	63.5725
1990	66.2913
1991	67.99295
1995	68.00455
1996	69.4694
1997	68.38561
1998	66.10532
1999	64.19063
2000	63.39733
2001	63.78172
2002	64.94405
2003	66.42497
2004	67.53556
2005	67.99444
2006	68.49719
2007	68.42295
2008	67.93907
2009	67.23842
2010	66.50346
2011	65.72625
2012	64.97501
2013	64.49621
2014	64.54362
2015	65.24976
2016	66.65977
2017	68.69807