Year	Percent
1990	16.67
1991	16.88
1992	17.09
1993	17.31
1994	17.52
1995	17.73
1996	17.94
1997	18.15
1998	18.36
1999	18.57
2000	18.78
2001	19.12
2002	19.46
2003	19.8
2004	20.14
2005	20.48
2006	20.64
2007	20.8
2008	20.96
2009	21.13
2010	21.29
2011	21.45
2012	21.61
2013	21.78
2014	21.94
2015	22.1