Year	Percent
1960	6.28641
1961	6.46873
1962	6.64959
1963	6.83505
1964	7.02451
1965	7.21566
1966	7.40966
1967	7.6065
1968	7.80739
1969	8.01159
1970	8.22161
1971	8.43726
1972	8.65899
1973	8.88412
1974	9.0915
1975	9.25325
1976	9.41563
1977	9.57745
1978	9.74155
1979	9.90847
1980	10.07991
1981	10.25419
1982	10.43352
1983	10.61779
1984	10.80831
1985	11.00342
1986	11.20574
1987	11.41485
1988	11.59117
1989	11.56997
1990	11.55072
1991	11.53309
1992	11.51804
1993	11.50473
1994	11.49494
1995	11.48872
1996	11.48693
1997	11.48843
1998	11.49464
1999	11.50514
2000	11.52056
2001	11.53974
2002	11.63092
2003	11.73463
2004	11.84735
2005	11.96845
2006	12.0998
2007	12.24091
2008	12.39298
2009	12.5549
2010	12.72876
2011	12.91448
2012	13.11241
2013	13.31945
2014	13.53564
2015	13.75914
2016	13.98967
2017	14.22778