Year	Percent
1990	53.25
1991	52.8
1992	52.35
1993	51.9
1994	51.45
1995	51
1996	50.55
1997	50.1
1998	49.65
1999	49.2
2000	48.75
2001	48.3
2002	47.85
2003	47.4
2004	46.95
2005	46.5
2006	45.73
2007	44.97
2008	44.2
2009	43.43
2010	42.66
2011	41.84
2012	41.02
2013	40.21
2014	39.39
2015	38.57