Year	Percent
1991	18.57
1992	18.05
1993	17.99
1994	19.31
1995	20.39
1996	20.73
1997	20.46
1998	20.16
1999	19.89
2000	19.74
2001	19.81
2002	18.68
2003	19.17
2004	19.14
2005	19.05
2006	19.14
2007	19.78
2008	19.64
2009	19.78
2010	18.75
2011	17.52
2012	17.1
2013	16.13
2014	16.5
2015	15.98
2016	14.9
2017	14.76
2018	14.61
2019	14.44