Year	Percent
1960	2.80781
1961	2.79435
1962	2.78683
1963	2.79295
1964	2.81724
1965	2.85208
1966	2.89034
1967	2.92221
1968	2.94497
1969	2.95467
1970	2.95649
1971	2.95467
1972	2.95742
1973	2.96995
1974	2.99479
1975	3.02661
1976	3.05741
1977	3.0795
1978	3.09142
1979	3.09105
1980	3.08159
1981	3.0694
1982	3.05645
1983	3.03957
1984	3.01842
1985	2.99455
1986	2.96797
1987	2.94138
1988	2.9196
1989	2.90366
1990	2.89066
1991	2.87676
1992	2.85849
1993	2.83618
1994	2.80932
1995	2.7782
1996	2.74353
1997	2.70735
1998	2.67007
1999	2.6329
2000	2.59397
2001	2.55403
2002	2.50962
2003	2.45625
2004	2.39276
2005	2.32253
2006	2.25256
2007	2.18465
2008	2.11406
2009	2.04139
2010	1.96875
2011	1.8956
2012	1.8277
2013	1.77287
2014	1.73395
2015	1.70643
2016	1.68246
2017	1.65637