Year	Percent
1960	21.48536
1961	21.61585
1962	21.68011
1963	21.63378
1964	21.60971
1965	21.62027
1966	21.6732
1967	21.76249
1968	21.85226
1969	21.89796
1970	21.93054
1971	21.94418
1972	21.94583
1973	21.94744
1974	21.96779
1975	21.99053
1976	21.99791
1977	22.03278
1978	22.08484
1979	22.13837
1980	22.18215
1981	22.2128
1982	22.24007
1983	22.27092
1984	22.29615
1985	22.31779
1986	22.33585
1987	22.34989
1988	22.36362
1989	22.38094
1990	22.38412
1991	22.45141
1992	22.42514
1993	22.413
1994	22.41467
1995	22.41881
1996	22.42468
1997	22.43039
1998	22.4329
1999	22.42496
2000	22.42574
2001	22.41654
2002	22.40774
2003	22.40314
2004	22.39265
2005	22.37788
2006	22.37605
2007	22.39184
2008	22.42134
2009	22.4539
2010	22.49134
2011	22.49889
2012	22.50657
2013	22.50706
2014	22.51562
2015	22.53834
2016	22.56519
2017	22.59501