Year	Percent
1992	38.84
1993	39.08
1994	39.33
1995	39.57
1996	39.81
1997	40.06
1998	40.3
1999	40.54
2000	40.79
2001	40.95
2002	41.11
2003	41.27
2004	41.43
2005	41.59
2006	41.67
2007	41.77
2008	41.87
2009	41.98
2010	42.06
2011	42.16
2012	42.25
2013	42.35
2014	42.45
2015	42.55