Year	Percent
1977	12.99903
1978	12.80076
1979	12.62904
1980	16.89253
1981	16.58271
1982	16.94714
1983	15.33384
1984	14.58853
1985	13.66642
1986	12.31069
1987	12.36974
1988	13.74851
1989	14.966
1990	15.11949
1991	15.39768
1992	16.96504
1993	17.25092
1994	16.83317
1995	17.6679
1996	17.75398
1997	17.95539
1998	18.60853
1999	18.6583
2000	15.74808
2001	15.2552
2002	15.26247
2003	13.34442
2004	13.0041
2005	12.80418
2006	13.1573
2007	13.4117
2008	12.71926
2009	11.36083
2010	11.70754
2011	12.83795
2012	12.75321
2013	12.22918
2014	12.41347
2015	11.34252
2016	11.51492
2017	11.53131