Year	Percent
1966	8.29639
1967	8.34306
1968	8.33819
1969	8.34219
1970	8.21478
1971	8.20961
1972	8.27703
1973	8.24219
1974	8.29774
1975	8.90756
1976	9.61153
1977	9.55313
1978	10.64453
1979	11.6462
1980	13.01519
1981	12.4832
1982	9.55221
1983	10.91974
1984	16.64569
1985	13.64697
1986	11.31767
1987	10.83739
1988	9.48881
1989	10.35203
1990	11.00949
1991	15.36001
1992	15.17003
1993	15.20011
1994	14.62553
1995	14.87393
1996	20.70366
1997	15.57435
1998	16.06871
1999	15.59421
2000	14.82267
2001	14.76682
2002	15.80698
2003	14.84903
2004	13.56058
2005	14.08249
2006	14.5264
2007	13.68989
2008	13.48765
2009	12.5303
2010	12.32885
2011	13.46228
2012	12.95219
2013	12.73545
2014	12.93522
2015	13.49657
2016	12.78283
2017	12.24386