Year	Percent
1990	91.69
1991	91.7
1992	91.79
1993	92.09
1994	92.13
1995	92.05
1996	91.95
1997	91.91
1998	91.9
1999	91.93
2000	91.95
2001	91.93
2002	91.84
2003	91.85
2004	91.78
2005	91.68
2006	91.58
2007	91.46
2008	91.36
2009	91.38
2010	91.36
2011	91.34
2012	91.27
2013	91.25
2014	91.23
2015	91.27
2016	91.35
2017	91.4
2018	91.49
2019	91.57