Year	Percent
1990	37.91
1991	38.04
1992	38.16
1993	38.29
1994	38.41
1995	38.53
1996	38.66
1997	38.78
1998	38.91
1999	39.03
2000	39.15
2001	39.28
2002	39.41
2003	39.53
2004	39.66
2005	39.79
2006	39.91
2007	40.04
2008	40.16
2009	40.29
2010	40.41
2011	40.54
2012	40.66
2013	40.78
2014	40.91
2015	41.03