Year	Percent
1990	4.21
1991	4.18
1992	4.16
1993	4.13
1994	4.11
1995	4.08
1996	4.06
1997	4.03
1998	4.01
1999	3.98
2000	3.96
2001	3.93
2002	3.9
2003	3.87
2004	3.84
2005	3.81
2006	3.78
2007	3.75
2008	3.72
2009	3.69
2010	3.66
2011	3.64
2012	3.61
2013	3.58
2014	3.55
2015	3.52