Year	Percent
1980	13.882
1981	13.17
1982	12.786
1983	12.24
1984	11.457
1985	13.356
1986	12.301
1987	10
1988	9.766
1989	9.009
1990	9.481
1991	9.661
1992	9.306
1993	11.949
1994	9.182
1995	7.799
1996	8.129
1997	9.2
1998	20.51
1999	17.462
2000	13.5575
2001	12.7418
2002	10.3837
2003	11.8433
2004	12.2226
2005	12.2494
2006	11.671
2007	11.3706
2008	11.5196
2009	11.9302
2010	11.207
2011	12.08
2012	9.7352
2013	9.7789
2014	11.1765
2015	11.3488
2016	11.0354
2017	11.2946