Year	Percent
1991	5.63
1992	22
1993	22.87
1994	24.19
1995	23.74
1996	25.57
1997	27.82
1998	28.55
1999	30.79
2000	31.11
2001	30.96
2002	23.59
2003	25.14
2004	22.05
2005	21.24
2006	19.92
2007	19.91
2008	18.94
2009	19.21
2010	20.24
2011	19.48
2012	19.38
2013	18.77
2014	18.28
2015	14.92
2016	13.3
2017	12.69