Year	Percent
1990	4.56
1991	4.89
1992	5.21
1993	5.54
1994	5.87
1995	6.19
1996	6.52
1997	6.85
1998	7.17
1999	7.5
2000	7.83
2001	8
2002	8.17
2003	8.35
2004	8.52
2005	8.7
2006	8.93
2007	9.17
2008	9.41
2009	9.65
2010	9.89
2011	10.02
2012	10.15
2013	10.28
2014	10.41
2015	10.54