Year	Percent
1960	50.61578
1961	50.258
1962	49.92759
1963	49.62486
1964	49.34948
1965	49.10146
1966	48.87525
1967	48.67526
1968	48.52554
1969	48.45559
1970	48.48368
1971	48.62142
1972	48.85192
1973	49.12676
1974	49.37995
1975	49.56985
1976	49.73036
1977	49.81403
1978	49.84457
1979	49.85665
1980	49.87681
1981	49.90671
1982	49.93951
1983	49.97553
1984	50.01412
1985	50.05249
1986	50.02844
1987	49.97925
1988	49.92905
1989	49.86801
1990	49.79149
1991	49.70061
1992	49.60101
1993	49.49579
1994	49.39145
1995	49.29388
1996	49.17401
1997	48.85305
1998	48.56385
1999	48.33591
2000	48.18651
2001	48.12571
2002	48.14012
2003	48.19519
2004	48.24172
2005	48.49453
2006	48.69247
2007	48.84352
2008	48.96088
2009	49.06593
2010	49.17614
2011	49.29375
2012	49.41337
2013	49.53273
2014	49.64837
2015	49.7581
2016	49.8622
2017	49.96297