Year	Percent
1990	67.37
1991	66.49
1992	65.6
1993	64.71
1994	63.83
1995	62.91
1996	62.03
1997	61.14
1998	60.26
1999	59.37
2000	58.49
2001	57.49
2002	56.49
2003	55.51
2004	54.51
2005	53.51
2006	53.2
2007	52.86
2008	52.54
2009	52.2
2010	51.89
2011	51.57
2012	51.26
2013	50.91
2014	50.6
2015	50.29