Year	Percent
1960	2.89586
1961	2.92627
1962	2.94404
1963	2.93505
1964	2.89309
1965	2.82938
1966	2.76365
1967	2.70497
1968	2.6471
1969	2.59209
1970	2.54098
1971	2.4887
1972	2.44072
1973	2.40795
1974	2.39361
1975	2.39123
1976	2.38825
1977	2.38022
1978	2.37249
1979	2.36413
1980	2.3526
1981	2.34208
1982	2.32418
1983	2.28563
1984	2.22206
1985	2.14224
1986	2.05947
1987	1.98312
1988	1.91264
1989	1.8511
1990	1.79719
1991	1.74195
1992	1.68836
1993	1.64805
1994	1.62386
1995	1.60965
1996	1.59943
1997	1.5833
1998	1.55487
1999	1.50973
2000	1.4529
2001	1.39539
2002	1.34137
2003	1.28568
2004	1.22887
2005	1.17255
2006	1.11461
2007	1.06002
2008	1.01686
2009	0.98845
2010	0.9703
2011	0.95601
2012	0.93892
2013	0.91702
2014	0.88756
2015	0.8528
2016	0.81756
2017	0.78449