Year	Percent
1990	14.33
1991	14.93
1992	15.54
1993	16.14
1994	16.75
1995	17.35
1996	17.95
1997	18.56
1998	19.16
1999	19.77
2000	20.37
2001	20.44
2002	20.52
2003	20.59
2004	20.67
2005	20.74
2006	20.82
2007	20.89
2008	20.97
2009	21.04
2010	21.11
2011	21.35
2012	21.59
2013	21.83
2014	22.07
2015	22.31