Year	Percent
1960	41.249
1961	41.853
1962	42.494
1963	43.137
1964	43.784
1965	44.431
1966	45.08
1967	45.732
1968	46.385
1969	47.038
1970	47.64
1971	47.919
1972	48.199
1973	48.479
1974	48.759
1975	49.038
1976	49.319
1977	49.598
1978	49.879
1979	50.159
1980	50.447
1981	50.786
1982	51.126
1983	51.465
1984	51.805
1985	52.143
1986	52.482
1987	52.82
1988	53.159
1989	53.497
1990	53.903
1991	54.757
1992	55.609
1993	56.456
1994	57.301
1995	58.141
1996	58.978
1997	59.807
1998	60.632
1999	61.451
2000	62.198
2001	62.497
2002	62.794
2003	63.091
2004	63.387
2005	63.682
2006	63.976
2007	64.268
2008	64.56
2009	64.851
2010	65.14
2011	65.437
2012	65.741
2013	66.052
2014	66.371
2015	66.696
2016	67.027
2017	67.365