Year	Percent
1990	91.7
1991	91.61
1992	91.69
1993	91.62
1994	91.74
1995	91.57
1996	91.43
1997	91.31
1998	91.2
1999	91.04
2000	90.87
2001	90.71
2002	90.54
2003	90.38
2004	90.2
2005	90.03
2006	89.86
2007	89.68
2008	89.49
2009	89.29
2010	89.08
2011	88.87
2012	88.64
2013	88.41
2014	88.46
2015	88.55
2016	88.65
2017	88.74
2018	88.84
2019	88.93