Year	Percent
1988	68.61
1989	68.91
1990	66.28
1991	67.43
1992	69.08
1993	67.75
1994	70.21
1995	71.86
1996	71.77
1997	70.8
1998	71.18
1999	69.14
2000	50.79
2001	50.07
2002	68.92
2003	51.61
2004	51.59
2005	52.06
2006	51.78
2007	52.88
2008	53.28
2009	52.65
2010	53.63
2011	54.15
2012	54.5
2013	54.27
2014	54.76
2015	54.15
2016	54.43
2017	53.75