Year	Percent
1991	61.94
1992	60.42
1993	58.41
1994	57.48
1995	55.8
1996	55.13
1997	55.18
1998	54.68
1999	52.37
2000	51.12
2001	50.47
2002	51.14
2003	52.2
2004	52.88
2005	53.91
2006	56.99
2007	57.89
2008	58
2009	52.63
2010	50.42
2011	53.66
2012	55.13
2013	55.99
2014	56.65
2015	58.35
2016	58.74
2017	60.09
2018	60.41
2019	60.68
2020	58.84