Year	Percent
1960	44.3101
1961	44.07088
1962	45.21521
1963	47.52302
1964	46.70893
1965	47.09952
1966	46.56956
1967	45.4625
1968	45.43224
1969	44.51669
1970	44.52172
1971	45.21201
1972	45.73395
1973	45.12351
1974	45.35973
1975	47.04796
1976	46.09764
1977	88.72433
1978	43.19403
1979	38.06884
1991	57.82505
1992	56.57387
1993	54.31233
1994	52.69074
1995	52.91569
1996	53.08098
1997	53.02347
1998	53.5206
1999	54.00303
2000	54.02749
2001	54.51577
2002	54.49087
2003	53.95988
2004	51.3879
2005	49.83629
2006	47.41707
2007	47.30507
2008	48.36343
2009	50.73652
2010	48.94358
2011	47.75827
2012	49.12926
2013	50.52605
2014	52.45416
2015	53.85217
2016	55.20228