Year	Percent
1981	9
1988	9.4
1990	9.1
1992	8.5
1994	9.6
1996	9.8
1998	9.9
1999	9.6
2000	9.6
2002	9.9
2004	9.7
2006	9.9
2007	10.3
2008	10.1
2009	10.3
2010	10.4
2011	11.1
2012	10.4
2013	10.8
2014	11
2015	11.3