Year	Percent
1960	74.54672
1961	74.58221
1962	73.90238
1963	73.47033
1964	70.5362
1965	69.23748
1966	68.89531
1967	68.99683
1968	68.12461
1969	67.33613
1970	65.06127
1971	64.14288
1972	62.19027
1973	62.67868
1974	63.17777
1975	63.08494
1976	62.40676
1977	62.54755
1978	63.16263
1979	61.49981
1980	59.89622
1981	60.50315
1982	61.8152
1983	60.68493
1984	60.02014
1985	63.12675
1986	62.6032
1987	62.84116
1988	61.51907
1989	62.31339
1990	64.20059
1991	62.83773
1992	62.48629
1993	62.0295
1994	61.85279
1995	61.63686
1996	62.10273
1997	62.65486
1998	62.75984
1999	63.08791
2000	60.64126
2001	63.58879
2002	64.06279
2003	64.49249
2004	63.31826
2005	64.55468
2006	65.36679
2007	66.56576
2008	68.82842
2009	68.49788
2010	68.30778
2011	69.47629
2012	69.50447
2013	70.99343
2014	70.43281
2015	69.9181
2016	70.04927
2017	70.43575