Year	%
1988	17.32
1989	41.88
1990	19.8
1991	19.81
1992	25.91
1993	19.14
1994	17.19
1995	14.79
1996	14.45
1997	13.46
1998	13.56
1999	14.86
2000	14.11
2001	11.99
2002	11.61
2003	11.46
2004	10.28
2005	9.73
2006	8.47
2007	8.8
2008	8.65
2009	8.18
2010	8.01
2011	8.09
2012	7.76
2013	7.7
2014	6.49
2015	7.02
2016	6.97
2017	6.19