Year	Percent
1991	27.43
1992	27.42
1993	27.35
1994	27.39
1995	27.34
1996	27.16
1997	27.05
1998	26.9
1999	26.7
2000	26.6
2001	26.46
2002	26.3
2003	26.22
2004	26.2
2005	26.23
2006	26.27
2007	26.31
2008	26.33
2009	26.14
2010	26.14
2011	26.15
2012	26.18
2013	26.24
2014	26.39
2015	26.56
2016	26.76
2017	27.02
2018	27.28
2019	27.5