Year	Percent
1960	50.776
1961	50.761
1962	50.746
1963	50.73
1964	50.715
1965	50.7
1966	50.685
1967	50.67
1968	50.654
1969	50.639
1970	50.624
1971	50.609
1972	50.593
1973	50.578
1974	50.563
1975	50.548
1976	50.532
1977	50.517
1978	50.502
1979	50.487
1980	50.472
1981	50.456
1982	50.441
1983	50.426
1984	50.411
1985	50.395
1986	50.38
1987	50.365
1988	50.35
1989	50.335
1990	50.319
1991	50.304
1992	49.998
1993	49.588
1994	49.177
1995	48.767
1996	48.356
1997	47.946
1998	47.536
1999	47.127
2000	46.717
2001	46.339
2002	45.972
2003	45.606
2004	45.24
2005	44.875
2006	44.511
2007	44.147
2008	43.783
2009	43.421
2010	43.059
2011	42.94
2012	42.957
2013	42.99
2014	43.041
2015	43.108
2016	43.192
2017	43.293