Year	Percent
1960	25.84435
1961	28.80886
1962	28.14446
1963	27.7897
1964	29.42346
1965	31.72093
1966	30.21243
1967	32.05674
1968	34.03175
1969	34.41781
1970	36.28499
1971	37.03093
1972	38.87928
1973	39.31319
1974	38.5236
1975	38.98542
1976	40.35471
1977	42.21339
1978	42.65756
1979	44.11288
1980	49.00967
1981	47.69776
1982	48.40262
1983	50.37466
1984	50.9208
1985	51.13847
1986	46.55585
1987	47.23916
1988	46.63504
1989	47.42423
1990	48.05434
1991	49.68797
1992	50.11364
1993	50.66238
1994	48.94323
1995	48.62635
1996	49.42298
1997	51.38815
1998	48.50855
1999	52.34106
2000	52.55462
2001	54.73244
2002	53.38833
2003	52.90701
2004	52.83795
2005	52.76823
2006	53.18884
2007	54.64392
2008	55.30764
2009	56.99433
2010	54.29444
2011	52.79714
2012	53.73439
2013	53.17945
2014	53.65825
2015	53.30841
2016	53.76306
2017	53.3144