Year	Percent
1990	72.71
1991	71.16
1992	69.6
1993	68.04
1994	66.48
1995	64.92
1996	63.36
1997	61.8
1998	60.24
1999	58.69
2000	57.13
2001	56.06
2002	54.98
2003	53.91
2004	52.84
2005	51.77
2006	50.69
2007	49.62
2008	48.55
2009	47.48
2010	46.4
2011	45.33
2012	44.26
2013	43.19
2014	42.11
2015	41.04