Year	Percent
1990	27.52
1991	27.21
1992	26.91
1993	26.62
1994	26.29
1995	25.79
1996	25.4
1997	24.93
1998	24.41
1999	23.87
2000	23.38
2001	23.04
2002	22.68
2003	22.38
2004	22.1
2005	21.78
2006	21.49
2007	21.26
2008	21.12
2009	20.98
2010	20.8
2011	20.68
2012	20.46
2013	20.27
2014	20.15
2015	20.03
2016	19.86
2017	19.74
2018	19.63
2019	19.51