Year	Percent
1960	48.4014
1961	48.21773
1962	48.56672
1963	48.6109
1964	48.83941
1965	48.50543
1966	48.73654
1967	49.43603
1968	50.76605
1969	50.25864
1970	51.23898
1971	52.15568
1972	51.29736
1973	50.05411
1974	48.30068
1975	48.46732
1976	48.9208
1977	49.18385
1978	47.74008
1979	45.4995
1980	43.07111
1981	45.12021
1982	46.53389
1983	47.47202
1984	48.26912
1985	47.45588
1986	47.37603
1987	48.8968
1988	48.29213
1989	49.0336
1990	50.4671
1991	52.38528
1992	55.33914
1993	55.43875
1994	55.2829
1995	56.07824
1996	57.05999
1997	57.83713
1998	58.19596
1999	59.25525
2000	59.07047
2001	58.45889
2002	58.26474
2003	60.08566
2004	60.12537
2005	60.10146
2006	60.71323
2007	60.1748
2008	59.0687
2009	60.50993
2010	61.01925
2011	60.87474
2012	61.28508
2013	61.16745
2014	61.02074
2015	61.36884
2016	61.02059
2017	61.49376