Year	Percent
1960	43.12016
1961	45.90883
1962	48.4914
1963	50.53842
1964	48.30266
1965	46.95122
1966	46.34146
1967	43.75676
1968	43.89474
1969	41.76418
1970	39.44888
1971	39.42731
1972	39.37844
1973	40.04131
1974	40.32219
1975	33.63792
1976	35.45595
1977	35.71335
1978	33.66397
1979	30.55971
1980	29.90722
1981	33.3222
1982	34.43854
1983	32.75265
1984	31.54775
1985	30.05257
1986	29.72601
1987	28.94681
1988	26.93763
1989	28.44992
1990	31.82627
1991	32.93139
1992	34.71323
1993	37.85699
1994	45.06848
1995	45.92732
1996	44.37818
1997	43.71665
1998	45.75183
1999	44.10798
2000	42.53951
2001	44.89224
2002	47.18619
2003	49.23179
2004	47.95428
2005	45.28387
2006	38.79476
2007	39.6875
2008	43.20657
2009	49.15614
2010	47.45462
2011	44.3934
2012	48.44389
2013	49.12796
2014	48.95541
2015	50.50977
2016	50.33058
2017	58.69392