Year	Percent
1960	10.435
1961	10.798
1962	11.204
1963	11.624
1964	12.058
1965	12.504
1966	12.965
1967	13.441
1968	13.932
1969	14.436
1970	14.957
1971	15.632
1972	16.455
1973	17.31
1974	18.202
1975	19.128
1976	20.092
1977	21.088
1978	22.122
1979	23.192
1980	24.298
1981	25.437
1982	26.612
1983	27.821
1984	29.065
1985	30.338
1986	31.643
1987	32.978
1988	34.343
1989	35.731
1990	37.144
1991	38.58
1992	40.039
1993	41.511
1994	43
1995	44.169
1996	45.346
1997	46.525
1998	47.71
1999	48.897
2000	50.087
2001	51.274
2002	52.461
2003	53.645
2004	54.827
2005	56
2006	56.764
2007	57.524
2008	58.282
2009	59.034
2010	59.783
2011	60.528
2012	61.268
2013	62.002
2014	62.731
2015	63.446
2016	64.149
2017	64.839