Year	Percent
1991	24.14
1992	23.91
1993	23.69
1994	23.5
1995	21.01
1996	18.74
1997	16.67
1998	17.31
1999	17.9
2000	18.54
2001	18.27
2002	17.92
2003	17.62
2004	17.4
2005	17.43
2006	17.55
2007	17.67
2008	17.76
2009	17.54
2010	17.51
2011	19.12
2012	20.68
2013	19.6
2014	19.92
2015	19.88
2016	19.85
2017	19.15
2018	18.16
2019	18.22