Year	Percent
1991	29.16
1992	28.99
1993	28.72
1994	28.42
1995	28.1
1996	28.02
1997	27.88
1998	27.7
1999	27.5
2000	27.33
2001	27.42
2002	27.45
2003	27.49
2004	27.54
2005	27.59
2006	27.85
2007	28.03
2008	28.14
2009	28.08
2010	28.08
2011	28.19
2012	24.66
2013	21.4
2014	23.48
2015	25.55
2016	26.24
2017	26.81
2018	27.27
2019	27.76