Year	Percent
1960	9.275
1961	9.856
1962	10.47
1963	11.118
1964	11.801
1965	12.519
1966	13.275
1967	14.069
1968	14.903
1969	15.776
1970	16.691
1971	17.647
1972	18.648
1973	19.689
1974	20.775
1975	21.904
1976	23.079
1977	24.293
1978	25.552
1979	26.676
1980	27.339
1981	28.01
1982	28.692
1983	29.384
1984	30.086
1985	30.796
1986	31.517
1987	32.246
1988	32.985
1989	33.73
1990	34.485
1991	35.247
1992	35.827
1993	36.136
1994	36.447
1995	36.758
1996	37.071
1997	37.385
1998	37.699
1999	38.015
2000	38.333
2001	38.65
2002	39.036
2003	39.536
2004	40.039
2005	40.543
2006	41.049
2007	41.558
2008	42.069
2009	42.58
2010	43.093
2011	43.608
2012	44.125
2013	44.642
2014	45.166
2015	45.695
2016	46.229
2017	46.768