Year	Percent
1991	29.54
1992	29.36
1993	29.08
1994	28.77
1995	28.45
1996	27.97
1997	27.53
1998	27.09
1999	26.66
2000	26.28
2001	26.25
2002	26.17
2003	26.09
2004	26.06
2005	26.08
2006	26.22
2007	26.65
2008	26.99
2009	27.15
2010	27.28
2011	27.39
2012	27.12
2013	26.78
2014	26.41
2015	25.99
2016	25.08
2017	24.01
2018	23.7
2019	23.37