Year	Percent
1960	9.22429
1961	9.36986
1962	9.52137
1963	9.68584
1964	9.87324
1965	10.08726
1966	10.33533
1967	10.61344
1968	10.90823
1969	11.19716
1970	11.39927
1971	11.43257
1972	11.44148
1973	11.44612
1974	11.47539
1975	11.54454
1976	11.66152
1977	11.81281
1978	11.9719
1979	12.09988
1980	12.17178
1981	12.17895
1982	12.13822
1983	12.07313
1984	12.05409
1985	12.14972
1986	12.27622
1987	12.42614
1988	12.5935
1989	12.76595
1990	12.93885
1991	13.11012
1992	13.28433
1993	13.46376
1994	13.6568
1995	13.86654
1996	14.09515
1997	14.33761
1998	14.59126
1999	14.84838
2000	15.07472
2001	15.21294
2002	15.35091
2003	15.48913
2004	15.63036
2005	15.77416
2006	15.9231
2007	16.07728
2008	16.24053
2009	16.41408
2010	16.603
2011	16.80768
2012	17.029
2013	17.26601
2014	17.51817
2015	17.78519
2016	18.06758
2017	18.36609