Year	Percent
1990	19.81
1991	19.82
1992	19.86
1993	19.91
1994	19.99
1995	20.02
1996	20.07
1997	20.11
1998	20.14
1999	20.18
2000	20.3
2001	20.37
2002	20.47
2003	20.58
2004	20.75
2005	20.96
2006	21.16
2007	21.41
2008	21.64
2009	21.75
2010	22.04
2011	22.27
2012	22.35
2013	22.65
2014	23.05
2015	23.48
2016	23.84
2017	24.12
2018	24.43
2019	24.75