Year	Percent
1991	70.47
1992	69.65
1993	68.51
1994	68.24
1995	68.71
1996	68.35
1997	68.87
1998	69.39
1999	69.46
2000	69.88
2001	68.01
2002	66.02
2003	63.96
2004	61.82
2005	59.61
2006	57.31
2007	54.93
2008	52.46
2009	49.87
2010	47.3
2011	47.08
2012	46.96
2013	46.88
2014	46.37
2015	46.03
2016	45.93
2017	45.88
2018	46.05
2019	45.9
2020	45.42