Year	Percent
1960	39.91031
1961	40.79656
1962	38.83197
1963	48.63813
1964	50.08993
1965	54.19521
1966	47.95322
1967	47.24771
1968	51.85185
1969	53.86064
1970	51.61627
1971	57.57433
1972	55.18561
1973	58.76439
1974	54.35556
1975	43.63442
1976	42.43789
1977	46.67478
1978	47.06638
1979	50.70407
1980	52.71934
1981	57.43232
1982	49.63623
1983	49.03695
1984	43.89556
1985	44.73983
1986	39.47458
1987	42.04204
1988	51.14638
1989	60.35528
1990	67.15657
1991	60.50441
1992	54.91465
1993	59.44874
1994	59.45218
1995	58.84731
1996	58.84538
1997	58.44001
1998	58.30422
1999	61.42002
2000	70.26341
2001	68.72539
2002	63.92405
2003	68.24656
2004	70.41595
2005	65.12049
2006	67.91633
2007	61.59407
2008	73.57959
2009	59.74466
2010	63.8931
2011	65.19624
2012	64.17465
2013	69.47496
2014	63.35027
2015	55.58361
2016	51.58048