Year	Percent
1960	8.50552
1961	8.41249
1962	8.56911
1963	8.32014
1964	7.63307
1965	7.63425
1966	7.47102
1967	6.86774
1968	7.03793
1969	7.54648
1970	7.75462
1971	7.64041
1972	8.06018
1973	8.41201
1974	8.40867
1975	6.89445
1976	8.48983
1977	10.31909
1978	10.47097
1979	11.18916
1980	10.70579
1981	10.40881
1982	15.33087
1983	19.00232
1984	17.38118
1985	15.41494
1986	17.34063
1987	19.49831
1988	19.92789
1989	18.99694
1990	18.60078
1991	16.36486
1992	15.2378
1993	12.2813
1994	13.38286
1995	24.14919
1996	26.00501
1997	24.33293
1998	24.59443
1999	24.63265
2000	25.40672
2001	22.66672
2002	22.55249
2003	24.36044
2004	28.41439
2005	30.37779
2006	27.32516
2007	27.52724
2008	27.7015
2009	27.155
2010	29.69767
2011	31.03671
2012	32.26557
2013	31.30565
2014	31.89686
2015	34.59116
2016	37.12241
2017	37.88006