Year	Percent
1990	11.25
1991	10.9
1992	10.55
1993	10.19
1994	9.84
1995	9.48
1996	9.13
1997	8.77
1998	8.42
1999	8.06
2000	7.71
2001	7.58
2002	7.45
2003	7.31
2004	7.18
2005	7.05
2006	7.61
2007	8.17
2008	8.73
2009	9.29
2010	9.85
2011	10.03
2012	10.21
2013	10.39
2014	10.57
2015	10.75