Year	Percent
1960	38.05084
1961	34.99795
1962	34.92224
1963	34.03866
1964	38.9777
1965	36.86636
1966	35.86929
1967	36.80539
1968	42.07263
1969	43.45724
1970	37.41671
1971	40.93886
1972	41.06733
1973	41.1303
1974	45.90589
1975	45.61222
1976	37.89126
1977	28.38236
1978	37.33076
1979	50.63205
1980	51.0402
1981	55.80659
1982	48.64243
1983	43.02751
1984	61.6103
1985	65.69387
1986	45.88652
1987	46.26744
1988	47.78635
1989	52.39798
1990	51.877
1991	51.39145
1992	63.21978
1993	38.7579
1994	55.84719
1995	56.376
1996	52.47433
1997	48.39559
1998	46.042
1999	45.19514
2000	50.72296
2001	49.26358
2002	49.0848
2003	51.53716
2004	51.77408
2005	55.21466
2006	60.61407
2007	61.51573
2008	71.6341
2009	52.40558
2010	49.58922
2011	53.47139
2012	51.87998
2013	52.72625
2014	53.49213
2015	46.20453
2016	44.93466
2017	45.51559