Year	Percent
1960	46.99355
1961	46.45639
1962	45.5294
1963	46.7126
1964	46.68453
1965	42.98568
1966	42.55735
1967	40.89208
1968	40.49261
1969	42.17233
1970	43.44737
1971	42.10514
1972	39.45842
1973	40.88031
1974	45.80557
1975	43.10013
1976	44.36636
1977	43.87432
1978	42.71015
1979	46.84188
1980	49.57186
1981	50.14614
1982	49.76873
1983	50.39329
1984	52.31722
1985	54.75889
1986	46.49984
1987	46.37645
1988	48.4099
1989	51.17608
1990	49.78264
1991	50.16567
1992	48.78433
1993	46.48218
1994	48.37446
1995	50.76489
1996	51.48315
1997	54.20113
1998	53.61057
1999	54.89589
2000	59.95902
2001	57.16306
2002	53.95965
2003	52.9454
2004	55.61239
2005	57.93728
2006	60.54692
2007	61.44828
2008	63.01601
2009	55.82602
2010	63.59103
2011	68.81677
2012	72.33463
2013	71.3142
2014	71.72312
2015	72.87115
2016	71.44032
2017	74.78272