Year	Percent
1960	44.39154
1961	31.93216
1962	31.31131
1963	33.06897
1964	35.32893
1965	35.09227
1966	37.87791
1967	33.88697
1968	31.1106
1969	35.41943
1970	40.27284
1971	41.91868
1972	42.76759
1973	42.82708
1974	42.43024
1975	45.35943
1976	45.03781
1977	46.70154
1978	47.71141
1979	46.9554
1980	48.05897
1981	45.97158
1982	44.6218
1983	44.22979
1984	42.93212
1985	42.71344
1986	43.51556
1987	43.31945
1988	43.52566
1989	42.49713
1990	41.03399
1991	41.48848
1992	43.11645
1993	46.1777
1994	46.16424
1995	46.75174
1996	47.10545
1997	47.10026
1998	45.79881
1999	45.36103
2000	45.53728
2001	44.79457
2002	44.45172
2003	45.62396
2004	45.9014
2005	47.02377
2006	47.55857
2007	46.86103
2008	46.93248
2009	45.88377
2010	46.39605
2011	46.40068
2012	45.2735
2013	44.00815
2014	43.10296
2015	40.93164
2016	39.88078
2017	40.45627