Year	Percent
1990	43.2
1991	42.93
1992	42.65
1993	42.38
1994	42.11
1995	41.84
1996	41.57
1997	41.3
1998	41.03
1999	40.75
2000	40.48
2001	40.21
2002	39.94
2003	39.67
2004	39.4
2005	39.12
2006	38.85
2007	38.58
2008	38.31
2009	38.04
2010	37.77
2011	38.65
2012	39.53
2013	40.41
2014	41.29
2015	42.17