Year	Percent
1960	31.1312
1961	39.24439
1962	35.04534
1963	25.41752
1964	35.07244
1965	31.98193
1966	38.88588
1967	37.92333
1968	42.01219
1969	45.89161
1970	49.63565
1971	46.82042
1972	39.28013
1973	33.11778
1974	66.00913
1975	43.40772
1976	47.30472
1977	41.46905
1978	63.97849
1979	50.0019
1980	51.06206
1981	46.23327
1982	50.14815
1983	45.47635
1984	51.24283
1985	48.40876
1986	43.98476
1987	41.36921
1988	43.65853
1989	39.66847
1990	33.47389
1991	33.44278
1992	26.93454
1993	24.38386
1994	30.54856
1995	32.43691
1996	33.28204
1997	28.97501
1998	29.68634
1999	28.87469
2000	34.38355
2001	33.80128
2002	36.51717
2003	43.36846
2004	38.56472
2005	40.0443
2006	38.20071
2007	37.91929
2008	35.49357
2009	36.74113
2010	40.16387
2011	39.43468
2012	46.67172
2013	52.70867
2014	44.49845
2015	42.21579
2016	42.82242
2017	40.47454