Year	Percent
1960	1.59489
1961	1.56677
1962	1.56339
1963	1.59673
1964	1.67328
1965	1.78565
1966	1.9356
1967	2.06805
1968	2.14363
1969	2.1306
1970	2.07703
1971	1.97554
1972	1.93769
1973	2.0574
1974	2.38565
1975	2.8327
1976	3.31157
1977	3.67189
1978	3.81677
1979	3.70299
1980	3.43084
1981	3.12672
1982	2.89834
1983	2.76018
1984	2.74974
1985	2.81724
1986	2.89107
1987	2.93496
1988	2.9583
1989	2.96341
1990	2.94933
1991	2.93941
1992	2.92377
1993	2.89637
1994	2.85313
1995	2.79797
1996	2.74555
1997	2.69071
1998	2.64077
1999	2.57869
2000	2.52234
2001	2.46424
2002	2.41551
2003	2.38271
2004	2.37499
2005	2.38237
2006	2.39064
2007	2.39672
2008	2.40363
2009	2.40872
2010	2.41254
2011	2.41757
2012	2.41882
2013	2.40661
2014	2.38337
2015	2.3477
2016	2.31119
2017	2.27544