Year	Percent
1990	49.7
1997	52.6
1999	54.8
2000	62.1
2001	57.4
2002	59.6
2004	53.1
2005	52.1
2006	48.1
2007	46.4
2008	39.2
2009	35.1
2011	28.3
2012	28.3
2013	26
2014	24.9
2015	25.6
2016	25