Year	Years
1989	8.1
1990	7.7
1991	7.4
1992	7.1
1993	6.8
1994	6.5
1995	6.2
1996	6
1997	5.8
1998	5.5
1999	5.3
2000	5.2
2001	5
2002	4.9
2003	4.7
2004	4.6
2005	4.5
2006	4.4
2007	4.3
2008	4.2
2009	4.1
2010	4
2011	3.9
2012	3.8
2013	3.7