Year	Percent
1991	69.53
1992	68.87
1993	68.24
1994	67.55
1995	66.73
1996	65.89
1997	64.14
1998	64.21
1999	63.74
2000	63.12
2001	62
2002	62.03
2003	61.22
2004	60.58
2005	59.56
2006	58.67
2007	57.75
2008	57.77
2009	57.65
2010	57.21
2011	55.92
2012	55.2
2013	56.97
2014	57.09
2015	56.84
2016	54.85
2017	54.75
2018	54.73
2019	52.23