Year	Percent
1960	29.76918
1961	29.87113
1962	25.53479
1963	27.30023
1964	27.9766
1965	36.40823
1966	37.02965
1967	32.68216
1968	36.76545
1969	38.41944
1970	37.26156
1971	33.58041
1972	33.75598
1973	36.63965
1974	43.23985
1975	40.91693
1976	44.43037
1977	42.3846
1978	38.83856
1979	44.98511
1980	47.05837
1981	46.98805
1982	46.63337
1983	43.89616
1984	53.51084
1985	46.9402
1986	39.02346
1987	35.87383
1988	35.44715
1989	39.97911
1990	41.51011
1991	42.09933
1992	45.59996
1993	43.19659
1994	43.69208
1995	43.18343
1996	41.46515
1997	43.49635
1998	43.68843
1999	45.52922
2000	51.64677
2001	50.18894
2002	44.1708
2003	39.75711
2004	41.90289
2005	41.79741
2006	43.75414
2007	42.11116
2008	48.73169
2009	41.6244
2010	42.30561
2011	44.38597
2012	42.88398
2013	41.45274
2014	41.87034
2015	39.91882
2016	36.8769
2017	37.96803