Year	Percent
1990	38.3
1991	38.29
1992	38.29
1993	38.28
1994	38.28
1995	38.27
1996	38.27
1997	38.26
1998	38.26
1999	38.25
2000	38.25
2001	38.24
2002	38.24
2003	38.23
2004	38.23
2005	38.22
2006	38.22
2007	38.21
2008	38.2
2009	38.2
2010	38.19
2011	38.19
2012	38.18
2013	38.18
2014	38.17
2015	38.17