Year	Percent
1960	25.10237
1961	25.15839
1962	25.1942
1963	25.13806
1964	25.0324
1965	24.93639
1966	24.8988
1967	24.89082
1968	24.92369
1969	24.98375
1970	25.09042
1971	25.16655
1972	25.18029
1973	25.21315
1974	25.24624
1975	25.2859
1976	25.35377
1977	25.43557
1978	25.52556
1979	25.61676
1980	25.70324
1981	25.80235
1982	25.87535
1983	25.94356
1984	26.01037
1985	26.06903
1986	26.12637
1987	26.17086
1988	26.15459
1989	26.12631
1990	26.11513
1991	26.08482
1992	26.04574
1993	26.01048
1994	25.99677
1995	26.01701
1996	26.14236
1997	26.25564
1998	26.37721
1999	26.49525
2000	26.61056
2001	26.69883
2002	26.75976
2003	26.82883
2004	26.89458
2005	26.92843
2006	26.93311
2007	26.91772
2008	26.88766
2009	26.85327
2010	26.78998
2011	26.60072
2012	26.58822
2013	26.63828
2014	26.75684
2015	26.78338
2016	26.82987
2017	26.91585