Year	Percent
1990	80.8
1991	80.55
1992	80.5
1993	80.27
1994	80.12
1995	80.03
1996	79.95
1997	79.84
1998	80.6
1999	81.34
2000	82.03
2001	82.7
2002	83.34
2003	83.94
2004	83.22
2005	82.47
2006	81.71
2007	80.92
2008	80.1
2009	79.25
2010	78.37
2011	77.49
2012	76.59
2013	75.65
2014	74.68
2015	73.69
2016	73.61
2017	73.52
2018	73.41
2019	73.31