Year	Percent
1960	52.81914
1961	49.18673
1962	48.62198
1963	48.53372
1964	49.69086
1965	48.15572
1966	46.54871
1967	44.50701
1968	44.52788
1969	45.51646
1970	45.46482
1971	43.42386
1972	40.97573
1973	45.72043
1974	51.65501
1975	47.14227
1976	48.32608
1977	46.86258
1978	44.21892
1979	47.03588
1980	50.7384
1981	54.42182
1982	53.11619
1983	53.29226
1984	55.14404
1985	56.39135
1986	50.1415
1987	46.77083
1988	48.2394
1989	51.228
1990	50.78075
1991	51.72501
1992	50.54487
1993	48.22983
1994	50.61016
1995	52.34668
1996	51.54014
1997	54.26778
1998	54.17482
1999	53.97083
2000	58.99751
2001	58.87846
2002	60.35489
2003	56.82863
2004	57.77719
2005	60.76441
2006	62.94602
2007	62.9879
2008	64.03785
2009	55.13516
2010	55.74378
2011	60.32712
2012	60.33769
2013	60.62464
2014	59.79577
2015	60.10906
2016	58.94417
2017	60.16059