Year	Percent
1960	45.184
1961	45.393
1962	45.603
1963	45.813
1964	46.023
1965	46.233
1966	46.637
1967	47.795
1968	48.956
1969	50.115
1970	51.276
1971	52.269
1972	52.611
1973	52.952
1974	53.294
1975	53.634
1976	53.975
1977	54.315
1978	54.655
1979	54.994
1980	55.333
1981	55.634
1982	55.794
1983	55.955
1984	56.115
1985	56.275
1986	56.427
1987	56.553
1988	56.678
1989	56.804
1990	56.929
1991	57.073
1992	57.293
1993	57.512
1994	57.731
1995	57.949
1996	58.173
1997	58.419
1998	58.664
1999	58.91
2000	59.155
2001	59.399
2002	59.649
2003	59.925
2004	60.202
2005	60.477
2006	60.738
2007	60.94
2008	61.141
2009	61.342
2010	61.542
2011	61.742
2012	61.942
2013	62.141
2014	62.34
2015	62.538
2016	62.737
2017	62.947