Year	Percent
1960	46.412
1961	46.557
1962	46.702
1963	46.848
1964	46.993
1965	47.139
1966	47.284
1967	47.43
1968	47.575
1969	47.721
1970	47.78
1971	47.735
1972	47.691
1973	47.646
1974	47.602
1975	47.557
1976	47.513
1977	47.469
1978	47.424
1979	47.299
1980	47.078
1981	46.858
1982	46.637
1983	46.417
1984	46.196
1985	45.976
1986	45.757
1987	45.537
1988	45.317
1989	45.16
1990	45.075
1991	44.99
1992	44.904
1993	44.819
1994	44.734
1995	44.794
1996	45.018
1997	45.241
1998	45.465
1999	45.689
2000	45.913
2001	46.137
2002	46.362
2003	46.587
2004	46.812
2005	47.052
2006	47.308
2007	47.581
2008	47.868
2009	48.172
2010	48.491
2011	48.825
2012	49.175
2013	49.541
2014	49.921
2015	50.317
2016	50.728
2017	51.153