Year	Percent
1991	31.01
1992	30.81
1993	30.76
1994	30.87
1995	30.82
1996	30.78
1997	30.64
1998	30.26
1999	29.85
2000	29.49
2001	29.13
2002	28.69
2003	28.24
2004	27.82
2005	27.47
2006	27.16
2007	26.83
2008	26.55
2009	26.08
2010	25.74
2011	25.46
2012	25.16
2013	24.72
2014	24.33
2015	23.31
2016	22.32
2017	20.28
2018	20.49
2019	20.43