Year	Percent
1960	5.18116
1961	5.2454
1962	5.30776
1963	5.42171
1964	5.70392
1965	5.99795
1966	6.30601
1967	6.62757
1968	6.96215
1969	7.306
1970	7.65959
1971	8.02166
1972	8.39366
1973	8.77433
1974	9.16779
1975	9.48733
1976	9.74487
1977	10.00431
1978	10.26837
1979	10.53719
1980	10.81219
1981	11.09713
1982	11.39559
1983	11.69762
1984	11.99097
1985	12.26708
1986	12.35567
1987	12.29038
1988	12.24861
1989	12.27883
1990	12.41214
1991	12.65891
1992	13.00357
1993	13.41291
1994	13.83491
1995	14.22095
1996	14.56259
1997	14.8575
1998	15.07199
1999	15.16755
2000	15.12807
2001	14.94518
2002	14.65625
2003	14.33357
2004	14.05465
2005	13.88249
2006	13.81719
2007	13.82075
2008	13.87313
2009	13.94404
2010	14.01549
2011	14.08514
2012	14.16026
2013	14.23887
2014	14.3235
2015	14.41418
2016	14.51036
2017	14.61036