Year	Percent
1991	23.72
1992	23.18
1993	23.62
1994	25.25
1995	25.31
1997	23.99
1998	24.15
1999	23.05
2000	23.22
2001	22.81
2002	22.72
2003	22.39
2004	22.83
2005	22.16
2006	22.44
2007	21.99
2008	21.62
2009	21.1
2010	20.88
2011	20.32
2012	20.21
2013	20.2
2014	20.74
2015	21.86
2016	20.16
2017	20.48