Year	Percent
1960	48.89395
1961	46.60737
1962	45.9426
1963	46.03269
1964	44.61096
1965	42.81079
1966	41.65148
1967	40.46763
1968	40.93763
1969	42.45681
1970	43.43649
1971	43.70221
1972	43.65921
1973	45.72389
1974	50.72497
1975	47.81304
1976	48.88716
1977	46.25765
1978	44.16402
1979	48.18742
1980	50.76422
1981	55.26754
1982	55.27822
1983	54.96408
1984	58.7964
1985	60.31291
1986	51.13197
1987	49.78778
1988	52.08987
1989	55.40707
1990	54.78559
1991	55.48459
1992	53.73983
1993	52.97064
1994	55.10868
1995	57.61094
1996	57.64568
1997	60.68155
1998	59.73441
1999	60.24038
2000	66.49296
2001	63.82348
2002	60.75074
2003	59.70936
2004	63.53583
2005	66.61657
2006	69.27895
2007	70.27361
2008	71.6426
2009	63.15445
2010	71.95398
2011	77.35644
2012	81.93622
2013	82.01021
2014	82.56537
2015	83.42558
2016	82.4485
2017	86.46381