Year	Percent
1980	5.3
1986	5.1
1987	4.6
1991	4.8
1992	4.6
1993	4.5
1994	4.4
1995	3.8
1996	3.5
1997	3.6
1998	3.4
1999	3.5
2000	3.2
2001	2.6
2002	2.8
2003	3.2
2004	3.5
2005	3.6
2006	3.7
2007	3.9
2008	4
2009	4
2010	4.6
2011	4.8
2012	4.9
2013	5
2014	5.1
2016	5