Year	Percent
1960	9.1
1961	9.459
1962	9.831
1963	10.216
1964	10.614
1965	11.026
1966	11.451
1967	11.891
1968	12.347
1969	12.815
1970	13.3
1971	13.598
1972	13.901
1973	14.209
1974	14.524
1975	14.844
1976	15.171
1977	15.502
1978	15.84
1979	16.183
1980	16.534
1981	16.889
1982	17.251
1983	17.619
1984	17.993
1985	18.373
1986	18.808
1987	19.323
1988	19.849
1989	20.385
1990	20.931
1991	21.489
1992	22.058
1993	22.636
1994	23.225
1995	23.76
1996	24.249
1997	24.743
1998	25.244
1999	25.752
2000	26.267
2001	26.787
2002	27.315
2003	27.849
2004	28.39
2005	28.936
2006	29.49
2007	30.051
2008	30.619
2009	31.194
2010	31.776
2011	32.364
2012	32.958
2013	33.559
2014	34.165
2015	34.777
2016	35.394
2017	36.016