Year	Percent
1991	30.1
1992	29.48
1993	29.16
1994	28.86
1995	27.99
1996	27.13
1997	26.31
1998	25.84
1999	25.33
2000	24.79
2001	24.43
2002	23.68
2003	23.08
2004	22.66
2005	22.97
2006	22.16
2007	22.34
2008	21.95
2009	20.46
2010	22.05
2011	18.28
2012	21.63
2013	21.3
2014	20.27
2015	18.77
2016	18.56
2017	18.55
2018	18.34
2019	18.42