Year	Percent
1991	27.83
1992	27.54
1993	27.49
1994	27.35
1995	27.86
1996	28.43
1997	29
1998	29.56
1999	30.11
2000	29.35
2001	28.62
2002	27.86
2003	27.16
2004	26.53
2005	25.95
2006	25.45
2007	24.97
2008	24.46
2009	23.77
2010	23.25
2011	22.2
2012	21.25
2013	20.35
2014	19.58
2015	20
2016	20.19
2017	20.29
2018	20.31
2019	20.31