Year	Percent
1960	14.06175
1961	15.02508
1962	12.63093
1963	13.83405
1964	13.7645
1965	15.26734
1966	15.13023
1967	13.8935
1968	14.4856
1969	13.33415
1970	13.22132
1971	12.93668
1972	11.97356
1973	11.02041
1974	13.21672
1975	14.73553
1976	13.38373
1977	14.65383
1978	14.59392
1979	15.36041
1980	15.91264
1981	16.74435
1982	16.83374
1983	15.62741
1984	15.00902
1985	17.30967
1986	18.08614
1987	17.09401
1988	16.64475
1989	16.97915
1990	17.07036
1991	16.19172
1992	16.41894
1993	17.89462
1994	18.52141
1995	19.88467
1996	19.39314
1997	18.9
1998	20.47485
1999	20.80216
2000	21.60415
2001	22.14891
2002	20.79123
2003	21.20985
2004	19.93653
2005	21.02931
2006	21.72581
2007	21.87698
2008	22.7391
2009	22.82648
2010	20.87387
2011	20.5051
2012	21.76811
2013	21.28586
2014	21.50408
2015	21.53442
2016	21.51845
2017	20.62262