Year	Percent
1991	79.75
1992	79.77
1993	79.81
1994	79.89
1995	80.03
1996	79.86
1997	79.72
1998	79.61
1999	79.5
2000	78.99
2001	78.48
2002	77.93
2003	77.35
2004	76.73
2005	76.13
2006	75.65
2007	75.14
2008	74.54
2009	73.65
2010	72.87
2011	72.25
2012	71.82
2013	71.52
2014	71.33
2015	71.1
2016	71.53
2017	71.82
2018	71.97
2019	72.02