Year	Percent
1991	90.07
1992	88.25
1993	85.44
1994	81.97
1995	78.79
1996	78.93
1997	78.16
1998	77.33
1999	76.45
2000	75.59
2001	74.81
2002	74.03
2003	73.31
2004	72.63
2005	71.94
2006	71.29
2007	70.65
2008	69.95
2009	69.07
2010	68.19
2011	67.27
2012	66.25
2013	65.15
2014	64.09
2015	63.71
2016	63.29
2017	63.06
2018	62.9
2019	62.63