Year	Percent
1991	55.94
1992	55.75
1993	55.5
1994	55.28
1995	55.2
1996	55.11
1997	55.12
1998	55.14
1999	55.04
2000	54.92
2001	54.75
2002	54.41
2003	54.06
2004	53.8
2005	53.65
2006	53.64
2007	53.74
2008	53.84
2009	53.75
2010	53.8
2011	53.77
2012	53.73
2013	53.67
2014	53.64
2015	53.59
2016	53.59
2017	53.62
2018	53.58
2019	53.55
2020	51.92