Year	Percent
1960	1.39208
1961	1.42859
1962	1.46575
1963	1.50349
1964	1.54194
1965	1.58081
1966	1.61996
1967	1.65917
1968	1.69928
1969	1.74092
1970	1.78489
1971	1.83154
1972	1.88006
1973	1.92738
1974	1.97014
1975	2.05746
1976	2.21937
1977	2.38453
1978	2.55559
1979	2.73533
1980	2.92691
1981	3.12984
1982	3.3454
1983	3.57468
1984	3.81987
1985	4.08055
1986	4.34627
1987	4.60693
1988	4.87868
1989	5.15074
1990	5.41981
1991	5.68218
1992	5.94505
1993	6.22158
1994	6.53493
1995	6.74144
1996	6.85541
1997	7.0002
1998	7.16939
1999	7.35107
2000	7.53748
2001	7.72554
2002	7.9194
2003	8.11869
2004	8.32507
2005	8.45876
2006	8.52927
2007	8.60146
2008	8.67577
2009	8.75103
2010	8.82879
2011	8.90865
2012	8.99114
2013	9.07768
2014	9.17
2015	9.26935
2016	9.37621
2017	9.49048