Year	Percent
1990	51.09
1991	50.47
1992	49.85
1993	49.23
1994	48.61
1995	47.99
1996	47.37
1997	46.75
1998	46.12
1999	45.5
2000	44.88
2001	44.44
2002	44
2003	43.55
2004	43.11
2005	42.67
2006	42.22
2007	41.78
2008	41.34
2009	40.89
2010	40.45
2011	40.01
2012	39.56
2013	39.12
2014	38.68
2015	38.23