Year	Percent
1960	46.96091
1961	47.56989
1962	46.66511
1963	46.30408
1964	45.82234
1965	45.55263
1966	45.71963
1967	45.08033
1968	45.45316
1969	45.59055
1970	45.40706
1971	45.30244
1972	45.47602
1973	44.98368
1974	44.97886
1975	45.28755
1976	45.62474
1977	45.95887
1978	46.35897
1979	46.54945
1980	46.82223
1981	47.28734
1982	47.81449
1983	48.37744
1984	49.17336
1985	49.72263
1986	50.3896
1987	51.03138
1988	51.66234
1989	52.27698
1990	52.16715
1991	50.55882
1992	51.16363
1993	53.11979
1994	55.21102
1995	57.35704
1996	58.39619
1997	58.27995
1998	58.28943
1999	58.14829
2000	57.95424
2001	57.9226
2002	58.09227
2003	58.18171
2004	58.0917
2005	58.00271
2006	57.913
2007	57.81933
2008	57.72753
2009	57.28142
2010	57.16188
2011	57.03111
2012	56.90368
2013	56.94838
2014	57.1529
2015	57.32559
2016	57.51545
2017	57.72352