Year	Percent
1977	14.90842
1978	16.30167
1979	17.59458
1980	19.12788
1981	18.72904
1982	16.79816
1983	14.50615
1984	14.40736
1985	14.50516
1986	13.64979
1987	13.50848
1988	14.39755
1989	15.85101
1990	13.39793
1991	13.94408
1992	14.65595
1993	15.0192
1994	14.6418
1995	14.67091
1996	13.85485
1997	13.88718
1998	14.06953
1999	15.06613
2000	15.06812
2001	14.30424
2002	13.81907
2003	13.7113
2004	14.99907
2005	15.95615
2006	17.10401
2007	13.37639
2008	14.04433
2009	14.09877
2010	12.34456
2011	12.09748
2012	11.97091
2013	12.22521
2014	11.09413
2015	11.18998
2016	11.44356
2017	11.46005