Year	Percent
1960	2.47272
1961	2.09121
1962	1.75145
1963	1.61891
1964	1.78214
1965	2.13545
1966	2.49834
1967	2.74277
1968	2.88689
1969	2.89921
1970	2.81546
1971	2.73201
1972	2.65363
1973	2.50381
1974	2.27445
1975	2.00251
1976	1.70586
1977	1.45023
1978	1.29779
1979	1.28278
1980	1.36268
1981	1.47199
1982	1.55199
1983	1.5956
1984	1.58278
1985	1.53256
1986	1.47006
1987	1.4263
1988	1.41206
1989	1.43789
1990	1.48587
1991	1.54565
1992	1.58021
1993	1.55645
1994	1.45717
1995	1.30902
1996	1.14268
1997	0.99931
1998	0.89898
1999	0.85997
2000	0.86328
2001	0.8803
2002	0.88177
2003	0.86127
2004	0.80798
2005	0.73339
2006	0.65435
2007	0.58922
2008	0.54331
2009	0.5241
2010	0.52423
2011	0.53007
2012	0.53145
2013	0.52946
2014	0.52048
2015	0.50657
2016	0.49278
2017	0.48111