Year	Percent
1988	7.02
1989	8.16
1990	11.32
1991	10.37
1992	11.63
1993	10.6
1994	11.04
1995	12.47
1996	10.93
1997	8.78
1998	10.75
1999	9.91
2000	18.55
2001	21.3
2002	8.64
2003	15
2004	19.41
2005	16.39
2006	19.46
2007	17.6
2008	17.59
2009	17.86
2010	15.75
2011	15.99
2012	16.78
2013	16.31
2014	14.41
2015	17.06
2016	19.35
2017	20.44