Year	Percent
1960	33.89588
1961	33.22279
1962	33.5128
1963	17.78306
1964	39.06518
1965	39.81982
1966	39.90064
1967	38.02394
1968	36.07684
1969	35.79193
1970	33.85475
1971	40.62798
1972	35.66819
1973	40.5339
1974	28.43691
1975	31.31488
1976	32.63802
1977	36.27934
1978	35.66395
1979	30.79429
1980	32.81354
1981	35.47404
1982	33.24081
1983	36.66332
1984	34.19869
1985	26.72109
1986	43.25443
1987	40.15918
1988	53.97426
1989	49.58443
1990	49.67913
1991	47.76411
1992	48.42879
1993	46.26741
1994	38.29495
1995	39.60488
1996	37.5412
1997	39.13029
1998	49.83743
1999	43.89063
2000	37.53118
2001	37.94173
2002	38.8653
2003	38.81635
2004	36.28491
2005	29.5651
2006	30.92131
2007	31.34844
2008	28.98312
2009	38.79766
2010	33.56816
2011	29.19852
2012	31.0831
2013	33.28117
2014	36.59646
2015	40.25401
2016	42.97042
2017	43.0186