Year	Percent
1992	39.63
1993	39.64
1994	39.65
1995	39.67
1996	39.68
1997	39.69
1998	39.7
1999	39.71
2000	39.73
2001	39.76
2002	39.8
2003	39.83
2004	39.86
2005	39.9
2006	40.04
2007	40.19
2008	40.33
2009	40.47
2010	40.62
2011	40.62
2012	40.62
2013	40.62
2014	40.62
2015	40.62