Year	Percent
1990	85.54
1991	86.58
1992	87.56
1993	88.47
1994	89.31
1995	89.46
1996	89.56
1997	89.7
1998	89.93
1999	90.17
2000	90.3
2001	90.42
2002	90.51
2003	90.51
2004	90.54
2005	90.6
2006	90.69
2007	90.73
2008	90.71
2009	90.68
2010	90.77
2011	90.87
2012	91.04
2013	91.14
2014	91.29
2015	91.43
2016	91.59
2017	91.69
2018	91.8
2019	91.91