Year	Percent
1960	11.66368
1961	10.61525
1962	10.10874
1963	9.95358
1964	9.85343
1965	9.52267
1966	9.01385
1967	9.00946
1968	9.35365
1969	9.27099
1970	9.65768
1971	8.71929
1972	8.82991
1973	9.4648
1974	10.57244
1975	9.62009
1976	9.86724
1977	10.2222
1978	11.03977
1979	12.45096
1980	12.97452
1981	12.93581
1982	10.31541
1983	9.42096
1984	9.55267
1985	10.33388
1986	13.43416
1987	13.38601
1988	18.53784
1989	19.06173
1990	19.70538
1991	19.27244
1992	20.27154
1993	15.54661
1994	17.32711
1995	22.17183
1996	24.41419
1997	24.44443
1998	26.40169
1999	25.98532
2000	27.02596
2001	24.49935
2002	24.14542
2003	25.84525
2004	30.00993
2005	31.98133
2006	28.76756
2007	29.26804
2008	30.07554
2009	28.81277
2010	31.06265
2011	32.43297
2012	33.50168
2013	32.45922
2014	33.07564
2015	36.63252
2016	39.10081
2017	39.68543