Year	Percent
1990	23.65
1991	23.69
1992	23.16
1993	22.63
1994	22.09
1995	21.56
1996	20.99
1997	20.43
1998	19.88
1999	19.34
2000	18.81
2001	18.28
2002	18.46
2003	18.63
2004	18.79
2005	18.95
2006	19.11
2007	19.28
2008	19.46
2009	19.64
2010	19.83
2011	20.04
2012	20.25
2013	20.46
2014	20.68
2015	20.9
2016	21.13
2017	21.38
2018	23.08
2019	24.6