Year	Percent
1991	39.59
1992	40.48
1993	40.16
1994	38.88
1995	39.38
1996	36.54
1997	36.4
1998	35.25
1999	31.42
2000	30.23
2001	28.99
2002	28.02
2003	27.82
2004	28.21
2005	28.79
2006	29.62
2007	30.51
2008	31.38
2009	28.97
2010	30.88
2011	31.79
2012	31.2
2013	30.68
2014	30.48
2015	30.62
2016	29.71
2017	28.85
2018	27.82
2019	26.03