Year	Percent
1960	64.72
1961	64.814
1962	64.863
1963	64.913
1964	64.962
1965	65.011
1966	65.061
1967	65.11
1968	65.159
1969	65.208
1970	65.258
1971	65.301
1972	65.311
1973	65.321
1974	65.331
1975	65.341
1976	65.351
1977	65.361
1978	65.371
1979	65.381
1980	65.391
1981	65.364
1982	65.1
1983	64.836
1984	64.57
1985	64.305
1986	64.037
1987	63.769
1988	63.5
1989	63.231
1990	62.96
1991	62.689
1992	62.417
1993	62.144
1994	61.87
1995	61.596
1996	61.32
1997	61.045
1998	60.768
1999	60.491
2000	60.213
2001	59.934
2002	59.655
2003	59.375
2004	59.094
2005	58.813
2006	58.532
2007	58.249
2008	57.966
2009	57.683
2010	57.399
2011	57.115
2012	57.147
2013	57.336
2014	57.526
2015	57.715
2016	57.905
2017	58.094