Year	Percent
1960	10.24347
1961	9.69546
1962	11.43449
1963	12.01055
1964	10.45456
1965	10.61662
1966	10.09893
1967	13.25246
1968	12.58834
1969	14.19449
1970	18.48559
1971	17.94464
1972	15.2795
1973	16.86301
1974	20.45915
1975	25.38793
1976	29.19775
1977	32.50939
1978	25.43424
1979	24.49269
1980	30.35348
1981	31.71888
1982	33.42852
1983	26.34856
1984	31.11285
1985	30.67795
1986	27.48216
1987	25.117
1988	24.44382
1989	30.27081
1990	31.06029
1991	27.32216
1992	27.71037
1993	26.4742
1994	25.66747
1995	25.39394
1996	24.47144
1997	24.92166
1998	27.80506
1999	25.83248
2000	26.3557
2001	27.6147
2002	27.21163
2003	29.03534
2004	30.93419
2005	30.27961
2006	30.90231
2007	33.88538
2008	39.08913
2009	35.04622
2010	34.07441
2011	35.77701
2012	35.01907
2013	34.67513
2014	32.17682
2015	30.24272
2016	33.05951
2017	33.16938