Year	Percent
1991	42.27
1992	42.45
1993	42.57
1994	42.6
1995	42.48
1996	42.71
1997	42.81
1998	42.79
1999	42.69
2000	42.63
2001	42.81
2002	42.91
2003	43
2004	43.07
2005	43.13
2006	41.67
2007	40.22
2008	38.76
2009	37.17
2010	35.72
2011	34.31
2012	32.94
2013	33
2014	33.04
2015	32.99
2016	33.01
2017	32.95
2018	32.8
2019	32.58