Year	Percent
1991	36.21
1992	37.1
1993	36.16
1994	37.28
1995	40.51
1996	46.59
1997	43.95
1998	46.32
1999	46.36
2000	46.21
2001	44.24
2002	43.56
2003	41.35
2004	43.22
2005	43.05
2006	42.64
2007	42.68
2008	40.73
2009	37.7
2010	36.75
2011	37.6
2012	32.52
2013	32.63
2014	30.04
2015	29.55
2016	33.19
2017	32.64
2018	32.12
2019	31.67