Year	Percent
1960	37.36
1961	38.781
1962	40.224
1963	41.684
1964	43.161
1965	44.646
1966	46.142
1967	47.646
1968	49.156
1969	50.442
1970	51.232
1971	52.022
1972	52.811
1973	53.597
1974	54.382
1975	55.165
1976	55.873
1977	56.262
1978	56.651
1979	57.039
1980	57.426
1981	57.812
1982	58.197
1983	58.532
1984	58.683
1985	58.834
1986	58.985
1987	59.135
1988	59.286
1989	59.434
1990	59.577
1991	59.719
1992	59.862
1993	60.004
1994	60.146
1995	60.288
1996	60.475
1997	60.838
1998	61.199
1999	61.559
2000	61.919
2001	62.276
2002	62.632
2003	62.987
2004	63.341
2005	63.965
2006	64.638
2007	65.306
2008	65.969
2009	66.624
2010	67.102
2011	67.565
2012	68.024
2013	68.479
2014	68.931
2015	69.379
2016	69.821
2017	70.256