Year	Percent
1990	23.15
1991	23.09
1992	23.01
1993	22.87
1994	22.64
1995	22.37
1996	22.18
1997	21.91
1998	21.6
1999	21.29
2000	21.1
2001	20.98
2002	20.89
2003	20.72
2004	20.66
2005	20.54
2006	20.11
2007	19.87
2008	19.52
2009	19.35
2010	19.12
2011	19.18
2012	19.27
2013	19.31
2014	19.23
2015	19.16
2016	19.02
2017	18.82
2018	18.62
2019	18.42