Year	Percent
1990	12.81
1991	12.91
1992	13
1993	13.1
1994	13.2
1995	13.3
1996	13.4
1997	13.5
1998	13.6
1999	13.7
2000	13.8
2001	13.67
2002	13.54
2003	13.41
2004	13.28
2005	13.14
2006	13.28
2007	13.42
2008	13.56
2009	13.7
2010	13.84
2011	13.96
2012	14.22
2013	14.34
2014	14.46
2015	14.58