Year	Percent
1960	1.35952
1961	1.34294
1962	1.3343
1963	1.35152
1964	1.40362
1965	1.47913
1966	1.56251
1967	1.63515
1968	1.68922
1969	1.71745
1970	1.72923
1971	1.74099
1972	1.7629
1973	1.7917
1974	1.83051
1975	1.878
1976	1.92292
1977	1.97116
1978	2.04008
1979	2.13357
1980	2.24081
1981	2.35117
1982	2.44783
1983	2.51959
1984	2.55978
1985	2.57781
1986	2.59025
1987	2.60586
1988	2.62172
1989	2.63969
1990	2.65915
1991	2.67692
1992	2.69299
1993	2.70965
1994	2.72732
1995	2.74591
1996	2.76489
1997	2.78369
1998	2.80294
1999	2.82227
2000	2.84189
2001	2.85887
2002	2.87599
2003	2.89843
2004	2.92756
2005	2.95919
2006	2.98907
2007	3.01181
2008	3.02496
2009	3.02645
2010	3.01924
2011	3.00894
2012	2.99725
2013	2.98148
2014	2.96198
2015	2.93969
2016	2.91561
2017	2.89107