Year	Percent
1960	12.129
1961	12.331
1962	12.535
1963	12.862
1964	13.677
1965	14.533
1966	15.433
1967	16.379
1968	17.373
1969	18.41
1970	19.496
1971	20.63
1972	21.814
1973	22.941
1974	23.675
1975	24.426
1976	25.193
1977	25.974
1978	26.772
1979	27.585
1980	28.414
1981	29.256
1982	30.113
1983	31.008
1984	32.007
1985	33.019
1986	34.049
1987	35.094
1988	36.155
1989	37.226
1990	38.312
1991	39.41
1992	40.52
1993	41.586
1994	42.472
1995	43.362
1996	44.258
1997	45.155
1998	46.057
1999	46.961
2000	47.868
2001	48.775
2002	49.683
2003	50.555
2004	51.288
2005	52.02
2006	52.751
2007	53.481
2008	54.211
2009	54.937
2010	55.662
2011	56.384
2012	57.105
2013	57.82
2014	58.528
2015	59.228
2016	59.918
2017	60.599