Year	Percent
1990	16.72
1991	15.51
1992	14.32
1993	13.14
1994	12.78
1995	12.51
1996	11.99
1997	11.56
1998	11.33
1999	11.06
2000	10.57
2001	10.08
2002	9.52
2003	9.16
2004	8.87
2005	8.58
2006	7.62
2007	7.3
2008	6.85
2009	6.29
2010	5.87
2011	5.59
2012	5.46
2013	5.26
2014	4.98
2015	4.79
2016	4.39
2017	4.23