Year	Percent
1990	5.45
1991	17.4
1992	16.22
1993	17.66
1994	16.75
1995	17
1996	16.1
1997	18.02
1998	15.01
1999	14.39
2000	12.57
2001	11.95
2002	11.89
2003	11.7
2004	11.19
2005	10.78
2006	10.33
2007	10.29
2008	9.94
2009	9.47
2010	9.35
2011	9.23
2012	8.87
2013	8.16
2014	8.03
2015	7.68
2016	7.22
2017	6.95