Year	Percent
1965	28.81101
1966	29.77881
1967	28.65806
1968	27.10347
1969	25.79379
1970	24.54895
1971	26.61451
1972	28.12648
1973	32.98297
1974	40.83127
1975	38.21625
1976	36.81688
1977	37.47297
1978	39.52992
1979	37.14127
1980	33.24492
1981	33.5878
1982	28.47034
1983	29.90928
1984	28.53654
1985	29.88677
1986	29.04596
1987	26.10232
1988	22.28502
1989	23.69051
1990	31.11864
1991	30.52766
1992	32.54233
1993	34.15499
1994	35.22593
1995	37.80625
1996	34.14087
1997	37.53526
1998	36.4857
1999	36.59409
2000	41.88282
2001	40.88145
2002	40.406
2003	42.31356
2004	43.87605
2005	44.44925
2006	47.51591
2007	52.05402
2008	53.9254
2009	42.12
2010	46.59061
2011	50.29486
2012	49.07942
2013	50.4996
2014	48.22737
2015	47.11908
2016	44.09497
2017	44.91005