Year	Percent
1960	13.15431
1961	13.33554
1962	13.53296
1963	13.74907
1964	13.98851
1965	14.25125
1966	14.54076
1967	14.85554
1968	15.19571
1969	15.55682
1970	15.94019
1971	16.34566
1972	16.60576
1973	16.86075
1974	17.11511
1975	17.3632
1976	17.60506
1977	17.83973
1978	18.071
1979	18.30007
1980	18.53024
1981	18.75881
1982	18.99061
1983	19.07773
1984	19.14714
1985	19.2344
1986	19.34418
1987	19.47463
1988	19.62351
1989	19.78409
1990	19.95578
1991	20.13681
1992	20.33019
1993	20.53796
1994	20.7682
1995	20.82114
1996	20.85523
1997	20.90834
1998	20.97819
1999	21.05946
2000	21.14866
2001	21.24277
2002	21.34247
2003	21.4453
2004	21.54981
2005	21.59269
2006	21.62321
2007	21.65246
2008	21.67677
2009	21.69009
2010	21.69097
2011	21.67786
2012	21.65428
2013	21.62596
2014	21.60304
2015	21.59155
2016	21.59344
2017	21.60767