Year	Percent
1960	7.946
1961	8.02
1962	8.095
1963	8.17
1964	8.246
1965	8.323
1966	8.4
1967	8.692
1968	8.994
1969	9.304
1970	9.625
1971	9.955
1972	10.295
1973	10.597
1974	10.837
1975	11.081
1976	11.331
1977	11.584
1978	11.843
1979	12.107
1980	12.377
1981	12.65
1982	12.93
1983	13.214
1984	13.504
1985	13.804
1986	14.118
1987	14.439
1988	14.766
1989	15.098
1990	15.437
1991	15.782
1992	16.133
1993	16.49
1994	16.854
1995	17.378
1996	18.234
1997	19.12
1998	20.039
1999	20.991
2000	21.977
2001	22.993
2002	24.044
2003	25.126
2004	26.242
2005	27.186
2006	27.748
2007	28.316
2008	28.893
2009	29.475
2010	30.064
2011	30.66
2012	31.264
2013	31.872
2014	32.487
2015	33.108
2016	33.736
2017	34.368