Year	Percent
1990	9.2
1991	5.93
1992	7.28
1993	9.25
1994	8.31
1995	8.26
1996	10.11
1997	12.06
1998	11.73
1999	10.65
2000	10.69
2001	11.54
2002	29.77
2003	31.38
2004	31.31
2005	30.64
2006	29.47
2007	26.29
2008	25.07
2009	25.25
2010	24.96
2011	24.68
2012	23.86
2013	23.52
2014	23.22
2015	23
2016	22.9
2017	21.7