Year	Percent
1991	25.71
1992	25.69
1993	25.66
1994	25.69
1995	25.75
1996	25.82
1997	25.53
1998	25.23
1999	24.9
2000	24.63
2001	24.35
2002	24.03
2003	23.75
2004	23.5
2005	23.25
2006	23.02
2007	22.77
2008	22.46
2009	23.13
2010	21.66
2011	20.22
2012	20.01
2013	19.71
2014	19.42
2015	19.13
2016	18.89
2017	18.65
2018	18.4
2019	18.13