Year	Percent
1960	4.75325
1961	5.00871
1962	5.28064
1963	5.57031
1964	5.78581
1965	5.95899
1966	6.13908
1967	6.32546
1968	6.51839
1969	6.71606
1970	6.91944
1971	7.13465
1972	7.40447
1973	7.67959
1974	7.95794
1975	8.23654
1976	8.51461
1977	8.79263
1978	9.0799
1979	9.38547
1980	9.71753
1981	10.07728
1982	10.46651
1983	10.88171
1984	11.11894
1985	11.36054
1986	11.60804
1987	11.86298
1988	12.12851
1989	12.40558
1990	12.69913
1991	12.95763
1992	13.13539
1993	13.25459
1994	13.37989
1995	13.51001
1996	13.64547
1997	13.78437
1998	13.92852
1999	14.0771
2000	14.23067
2001	14.38724
2002	14.54889
2003	14.71428
2004	14.88338
2005	15.05355
2006	15.20481
2007	15.29893
2008	15.39393
2009	15.48852
2010	15.58557
2011	15.68467
2012	15.78709
2013	15.89194
2014	16.00287
2015	16.12022
2016	16.2445
2017	16.37572