Year	Percent
1990	23.4
1991	23.6
1992	23.73
1993	23.81
1994	23.77
1995	23.7
1996	23.6
1997	23.44
1998	23.28
1999	23.12
2000	22.94
2001	22.79
2002	22.68
2003	22.6
2004	22.43
2005	22.32
2006	22.37
2007	22.32
2008	22.27
2009	22.23
2010	22.17
2011	22.15
2012	22.09
2013	22.04
2014	21.98
2015	21.95
2016	21.95
2017	21.94
2018	21.94
2019	21.91