Year	Percent
1960	8.99997
1961	9.147
1962	9.30447
1963	9.4708
1964	9.6399
1965	9.81958
1966	9.97111
1967	10.09861
1968	10.21959
1969	10.33564
1970	10.46518
1971	10.60745
1972	10.76105
1973	10.91026
1974	11.04554
1975	11.20322
1976	11.3691
1977	11.52691
1978	11.73492
1979	11.94391
1980	12.12447
1981	12.31563
1982	12.51482
1983	12.72312
1984	12.93725
1985	13.18529
1986	13.31252
1987	13.28789
1988	13.2679
1989	13.41895
1990	13.65798
1991	13.78867
1992	13.93223
1993	13.98566
1994	13.9354
1995	13.90002
1996	13.87434
1997	13.86188
1998	13.8574
1999	13.83816
2000	13.80957
2001	13.98915
2002	14.45268
2003	14.73845
2004	14.99791
2005	15.26124
2006	15.49219
2007	15.71148
2008	15.95687
2009	16.19638
2010	16.44198
2011	16.68846
2012	16.92833
2013	17.13311
2014	17.30674
2015	17.49432
2016	17.69525
2017	17.90336