Year	Percent
1960	47.26
1961	47.297
1962	47.335
1963	47.372
1964	47.341
1965	47.109
1966	46.877
1967	46.644
1968	46.412
1969	46.18
1970	45.948
1971	45.716
1972	46.76
1973	49.087
1974	51.421
1975	53.749
1976	56.064
1977	58.346
1978	60.597
1979	62.803
1980	64.96
1981	65.035
1982	65.11
1983	65.184
1984	65.259
1985	65.334
1986	65.408
1987	65.483
1988	65.557
1989	65.632
1990	65.706
1991	65.78
1992	65.854
1993	65.928
1994	66.002
1995	66.076
1996	66.15
1997	66.223
1998	66.297
1999	66.371
2000	66.444
2001	66.517
2002	66.591
2003	66.664
2004	66.737
2005	66.682
2006	66.615
2007	66.547
2008	66.479
2009	66.412
2010	66.344
2011	66.276
2012	66.208
2013	66.14
2014	66.089
2015	66.056
2016	66.04
2017	66.041