Year	Percent
1960	1.16993
1961	1.20994
1962	1.25533
1963	1.30369
1964	1.3517
1965	1.39635
1966	1.43678
1967	1.47374
1968	1.50882
1969	1.54417
1970	1.58171
1971	1.66358
1972	1.7549
1973	1.85088
1974	1.95124
1975	2.05515
1976	2.16292
1977	2.27428
1978	2.39008
1979	2.44696
1980	2.4951
1981	2.54589
1982	2.6007
1983	2.65469
1984	2.70179
1985	2.73933
1986	2.76036
1987	2.77192
1988	2.80067
1989	2.87848
1990	3.02858
1991	3.27863
1992	3.73225
1993	4.30959
1994	4.90798
1995	5.39713
1996	5.6803
1997	5.81156
1998	5.87848
1999	5.98401
2000	6.19941
2001	6.53922
2002	6.9861
2003	7.16636
2004	7.30878
2005	7.42593
2006	7.51407
2007	7.58648
2008	7.6492
2009	7.71066
2010	7.77858
2011	7.85265
2012	7.9304
2013	8.01071
2014	8.0941
2015	8.18053
2016	8.27022
2017	8.36375