Year	Percent
1990	57.29
1991	56.45
1992	55.6
1993	54.76
1994	53.91
1995	53.07
1996	52.22
1997	51.38
1998	50.53
1999	49.69
2000	48.84
2001	48
2002	47.15
2003	46.3
2004	45.46
2005	44.61
2006	43.77
2007	42.92
2008	42.08
2009	41.23
2010	40.39
2011	39.58
2012	38.77
2013	37.97
2014	37.16
2015	36.35