Year	Percent
1990	12.89
1991	13
1992	13.1
1993	13.21
1994	13.31
1995	13.42
1996	13.52
1997	13.63
1998	13.73
1999	13.84
2000	13.94
2001	14.28
2002	14.61
2003	14.94
2004	15.27
2005	15.61
2006	16.1
2007	16.6
2008	17.09
2009	17.58
2010	18.08
2011	18.35
2012	18.63
2013	18.91
2014	19.18
2015	19.46