Year	Percent
1981	5.4
1988	6.1
1990	5.9
1992	5.4
1994	6.1
1996	6.2
1998	6.4
1999	6.1
2000	6.2
2002	6.3
2004	6.1
2006	6
2007	6.5
2008	6.4
2009	6.5
2010	6.6
2011	7.2
2012	6.6
2013	6.9
2014	7.1
2015	7.5