Year	Percent
1990	38.5
1991	38.24
1992	37.85
1993	37.57
1994	37.38
1995	37.11
1996	36.94
1997	36.61
1998	36.53
1999	36.76
2000	36.79
2001	37.1
2002	37.3
2003	37.5
2004	37.69
2005	37.91
2006	37.99
2007	38.04
2008	38.21
2009	38.22
2010	38.22
2011	38.32
2012	38.42
2013	38.48
2014	38.51
2015	38.42
2016	38.52
2017	38.31
2018	38.08
2019	38.19