Year	Percent
1991	38.31
1992	38.22
1993	38.27
1994	38.43
1995	38.48
1996	38.57
1997	38.61
1998	38.59
1999	38.56
2000	38.56
2001	38.56
2002	38.53
2003	38.52
2004	38.52
2005	38.53
2006	38.55
2007	38.55
2008	38.63
2009	38.56
2010	38.57
2011	38.68
2012	38.8
2013	39.01
2014	39.22
2015	39.26
2016	39.26
2017	37.08
2018	37.39
2019	37.49
2020	35.66