Year	Percent
1960	2.59316
1961	2.62226
1962	2.64831
1963	2.66855
1964	2.68181
1965	2.69016
1966	2.69199
1967	2.69371
1968	2.70383
1969	2.72495
1970	2.75012
1971	2.77794
1972	2.79384
1973	2.7833
1974	2.74067
1975	2.67858
1976	2.60552
1977	2.54299
1978	2.50786
1979	2.50871
1980	2.52975
1981	2.56255
1982	2.57778
1983	2.55079
1984	2.47042
1985	2.35955
1986	2.22895
1987	2.12235
1988	2.07951
1989	2.11899
1990	2.20635
1991	2.30891
1992	2.3713
1993	2.35997
1994	2.25414
1995	2.08697
1996	1.90707
1997	1.75269
1998	1.6247
1999	1.53566
2000	1.47499
2001	1.42586
2002	1.37281
2003	1.31516
2004	1.24859
2005	1.18102
2006	1.10811
2007	1.05309
2008	1.04677
2009	1.10215
2010	1.19711
2011	1.30741
2012	1.39597
2013	1.44091
2014	1.42593
2015	1.36877
2016	1.30137
2017	1.24488