Year	Percent
1991	74.33
1992	73.84
1993	72.88
1994	71.96
1995	71.02
1996	69.91
1997	68.59
1998	67.22
1999	65.57
2000	64.01
2001	61.26
2002	58.64
2003	56.17
2004	54.69
2005	53.47
2006	52.74
2007	52.41
2008	51.77
2009	51.13
2010	50.39
2011	49.55
2012	48.21
2013	46.68
2014	45.11
2015	43.79
2016	42.81
2017	42.07
2018	41.49
2019	40.53