Year	Percent
1990	18.3
1995	40.3
1997	35.3
1999	37.2
2001	36.2
2002	47.4
2003	40.5
2004	38.5
2005	35
2006	39.5
2007	36.1
2008	33
2009	31.9
2010	30
2011	28.3
2012	23.5
2013	20.4
2014	19.3
2015	20
2016	20.1