Year	Percent
1991	66.08
1992	65.96
1993	65.3
1994	64.63
1995	63.92
1996	63.14
1997	62.32
1998	61.46
1999	60.55
2000	59.61
2001	58.64
2002	57.64
2003	55.54
2004	53.44
2005	51.35
2006	49.28
2007	47.22
2008	45.2
2009	43.14
2010	41.2
2011	41.6
2012	41.42
2013	41.19
2014	41.01
2015	40.81
2016	40.66
2017	40.48
2018	40.26
2019	40