Year	Percent
1991	57.83
1992	56.03
1993	53.57
1994	53
1995	54.01
1996	53.19
1997	54.3
1998	55.37
1999	55.45
2000	56.3
2001	54.48
2002	52.57
2003	50.66
2004	48.74
2005	46.78
2006	44.81
2007	42.81
2008	40.77
2009	38.64
2010	36.6
2011	36.3
2012	35.99
2013	35.75
2014	34.55
2015	33.77
2016	33.6
2017	33.52
2018	33.92
2019	33.59