Year	Percent
1981	6.2
1982	6
1983	5.9
1984	6
1985	6.5
1986	6
1987	5.7
1988	5.3
1989	5
1990	5.5
1992	7.1
1993	5.8
1995	5.8
1996	5.7
1997	5.7
1998	5.8
1999	6
2001	6
2002	6.1
2003	6.2
2004	6.5
2005	6.5
2006	6.7
2007	6.9
2008	7.1
2009	7.2
2011	7.5
2012	7.6
2013	7.6
2014	7.8
2015	7.9