Year	Percent
1960	47.679
1961	48.021
1962	48.364
1963	48.706
1964	49.049
1965	49.392
1966	49.734
1967	50.077
1968	50.42
1969	50.763
1970	51.106
1971	51.487
1972	51.882
1973	52.275
1974	52.669
1975	53.063
1976	53.456
1977	53.848
1978	54.24
1979	54.632
1980	55.259
1981	57.358
1982	59.435
1983	61.478
1984	63.484
1985	65.439
1986	67.345
1987	69.197
1988	70.99
1989	72.716
1990	74.343
1991	75.537
1992	76.694
1993	77.81
1994	78.888
1995	79.928
1996	80.93
1997	81.89
1998	82.814
1999	83.7
2000	84.55
2001	85.362
2002	86.007
2003	86.608
2004	87.188
2005	87.745
2006	88.281
2007	88.797
2008	89.294
2009	89.77
2010	90.228
2011	90.668
2012	91.09
2013	91.483
2014	91.851
2015	92.195
2016	92.517
2017	92.817