Year	Percent
1990	20.04
1991	20.17
1992	20.3
1993	20.43
1994	20.56
1995	20.69
1996	20.82
1997	20.96
1998	21.09
1999	21.22
2000	21.39
2001	21.54
2002	21.68
2003	21.83
2004	21.98
2005	22.13
2006	22.27
2007	22.41
2008	22.55
2009	22.46
2010	22.6
2011	22.65
2012	22.7
2013	22.75
2014	22.8
2015	22.85