Year	Percent
1990	19.54
1991	19.98
1992	20.45
1993	20.93
1994	21.44
1995	21.97
1996	22.54
1997	23.13
1998	23.75
1999	24.4
2000	25.08
2001	24.68
2002	24.28
2003	23.88
2004	23.48
2005	23.08
2006	22.68
2007	22.28
2008	21.88
2009	21.48
2010	21.09
2011	21.1
2012	21.11
2013	21.12
2014	21.12
2015	21.12
2016	21.12
2017	21.13
2018	21.14
2019	21.15