Year	Percent
1960	40.56076
1961	41.32549
1962	42.82244
1963	44.34025
1964	45.90823
1965	47.51517
1966	48.60197
1967	49.47951
1968	50.67983
1969	51.01508
1970	51.84
1971	52.41773
1972	52.88593
1973	53.66544
1974	53.87649
1975	54.25914
1976	54.64215
1977	54.74277
1978	54.87773
1979	55.04843
1980	55.25385
1981	55.40294
1982	55.55973
1983	55.71576
1984	55.89974
1985	56.09622
1986	56.39932
1987	56.80629
1988	57.25487
1989	57.71541
1990	58.22063
1991	58.50265
1992	58.74008
1993	58.97838
1994	59.16276
1995	59.32347
1996	59.35427
1997	59.32535
1998	59.27839
1999	59.28596
2000	59.30445
2001	59.50079
2002	59.79041
2003	60.10822
2004	60.55497
2005	61.03817
2006	61.39071
2007	61.6773
2008	62.0103
2009	62.38554
2010	62.74801
2011	63.05547
2012	63.28528
2013	63.50608
2014	63.72078
2015	63.91955
2016	64.12532
2017	64.36373