Year	Percent
1990	60.45
1991	60.45
1992	60.49
1993	60.57
1994	60.66
1995	60.76
1996	60.84
1997	60.93
1998	61.01
1999	61.09
2000	61.16
2001	61.29
2002	61.41
2003	61.52
2004	62.07
2005	61.22
2006	60.26
2007	59.17
2008	58.05
2009	57.71
2010	57.06
2011	56.3
2012	55.5
2013	54.66
2014	53.8
2015	52.96
2016	52.1
2017	51.08
2018	50.17
2019	49.35