Year	Percent
1991	71.72
1992	71.46
1993	71.1
1994	70.56
1995	70.13
1996	69.73
1997	69.3
1998	68.85
1999	68.33
2000	67.81
2001	67.27
2002	66.67
2003	66.08
2004	65.53
2005	65.01
2006	64.63
2007	64.22
2008	63.79
2009	63.27
2010	62.85
2011	62.34
2012	61.83
2013	61.28
2014	60.71
2015	60.1
2016	59.51
2017	58.91
2018	58.33
2019	57.89