Year	Percent
1960	40.07297
1961	39.62312
1962	39.32502
1963	38.84873
1964	38.97275
1965	49.96253
1966	51.77627
1967	51.39129
1968	48.98543
1969	51.90427
1970	48.68045
1971	47.90835
1972	47.52979
1973	47.74737
1974	48.25212
1975	51.05423
1976	50.84037
1977	51.30532
1978	51.74789
1979	52.94696
1980	54.8214
1981	55.43011
1982	54.6989
1983	54.13467
1984	49.84951
1985	49.59493
1986	48.53256
1987	48.34495
1988	45.22897
1989	45.63108
1990	46.64006
1991	46.15504
1992	47.08603
1993	46.50668
1994	48.80876
1995	50.29425
1996	51.80943
1997	52.60643
1998	54.65361
1999	52.39025
2000	45.26796
2001	50.38035
2002	51.87289
2003	54.18421
2004	54.05528
2005	53.42835
2006	51.78038
2007	51.29113
2008	49.53399
2009	52.05995
2010	51.14921
2011	49.30743
2012	48.97519
2013	49.25344
2014	49.34507
2015	51.37335
2016	51.3007
2017	52.11351