Year	Percent
1992	21.994
1993	26.815
1994	24.569
1995	20.713
1996	20.9832
1997	18.8386
1998	17.1011
1999	13.5037
2000	13.6659
2001	11.5566
2002	12.327
2003	13.4619
2004	14.5768
2005	19.633
2006	18.6488
2007	17.4099
2008	18.8737
2009	27.8533
2010	27.7582
2011	26.9722
2012	29.0735
2013	25.5925
2014	19.9765
2015	18.2833
2016	12.9421
2017	9.7123