Year	Percent
1991	42.59
1992	42.78
1993	42.94
1994	43.18
1995	43.46
1996	43.71
1997	43.59
1998	43.46
1999	43.31
2000	43.22
2001	43.15
2002	43.03
2003	42.94
2004	42.88
2005	42.81
2006	42.77
2007	42.69
2008	42.54
2009	43.22
2010	41.92
2011	40.61
2012	40.44
2013	40.34
2014	40.31
2015	40.26
2016	40.23
2017	40.24
2018	40.32
2019	40.4
2020	38.61