Year	Percent
1960	36.762
1961	37.059
1962	37.357
1963	37.656
1964	37.957
1965	38.257
1966	38.559
1967	38.862
1968	39.166
1969	39.47
1970	39.776
1971	40.082
1972	40.389
1973	40.696
1974	41.004
1975	41.314
1976	41.624
1977	42.446
1978	43.442
1979	44.443
1980	45.451
1981	46.459
1982	47.472
1983	48.486
1984	49.504
1985	50.519
1986	51.535
1987	52.549
1988	53.563
1989	54.571
1990	55.577
1991	56.579
1992	57.541
1993	58.079
1994	58.615
1995	59.15
1996	59.682
1997	60.212
1998	60.739
1999	61.264
2000	61.787
2001	62.306
2002	62.783
2003	63.248
2004	63.711
2005	64.17
2006	64.628
2007	65.082
2008	65.535
2009	65.984
2010	66.43
2011	66.874
2012	67.315
2013	67.699
2014	68.047
2015	68.393
2016	68.738
2017	69.08