Year	Percent
1991	33.74
1992	33.72
1993	33.6
1994	32.78
1995	33.06
1996	32.23
1997	32.23
1998	31.71
1999	31.52
2000	31.56
2001	31.65
2002	32.01
2003	31.94
2004	32.32
2005	32.03
2006	31.27
2007	31.46
2008	29.96
2009	30.38
2010	29.79
2011	29.58
2012	28.17
2013	26.82
2014	25.33
2015	23.86
2016	22.21
2017	20.93
2018	20.75
2019	20.57