Year	Percent
1990	6.51
1991	11.08
1992	9.37
1993	12.22
1994	9.86
1995	9.24
1996	9.1
1997	8.89
1998	7.89
1999	7.37
2000	6.13
2001	6
2002	5.65
2003	5.45
2004	5.19
2005	5.08
2006	4.6
2007	4.52
2008	4.5
2009	4.65
2010	4.79
2011	4.33
2012	4.43
2013	4.26
2014	4.02
2015	3.86
2016	3.46
2017	3.32