Year	Percent
1960	34.254
1961	34.329
1962	34.404
1963	34.606
1964	35.197
1965	35.791
1966	36.39
1967	36.993
1968	37.601
1969	38.212
1970	38.827
1971	39.445
1972	40.068
1973	40.655
1974	41.002
1975	41.349
1976	41.698
1977	42.046
1978	42.396
1979	42.747
1980	43.099
1981	43.45
1982	43.803
1983	44.156
1984	44.542
1985	45.445
1986	46.353
1987	47.264
1988	48.177
1989	49.089
1990	50.003
1991	50.917
1992	51.832
1993	52.743
1994	53.653
1995	54.561
1996	55.467
1997	56.367
1998	57.264
1999	58.157
2000	59.052
2001	60.41
2002	61.753
2003	63.08
2004	64.388
2005	65.672
2006	66.935
2007	68.174
2008	69.39
2009	70.575
2010	71.736
2011	72.868
2012	73.946
2013	74.97
2014	75.941
2015	76.862
2016	77.735
2017	78.56