Year	Percent
1990	51.44
1991	50.97
1992	50.51
1993	50.04
1994	49.58
1995	49.11
1996	48.65
1997	48.18
1998	47.72
1999	47.25
2000	46.79
2001	46.32
2002	45.85
2003	45.39
2004	44.92
2005	44.46
2006	43.99
2007	43.53
2008	43.06
2009	42.6
2010	42.13
2011	41.67
2012	41.2
2013	40.74
2014	40.27
2015	39.8