Year	Percent
1990	55.27
1991	55.47
1992	55.64
1993	55.73
1994	55.6
1995	55.87
1996	55.38
1997	54.85
1998	54.42
1999	54.06
2000	53.85
2001	52.69
2002	51.78
2003	51.14
2004	50.42
2005	49.72
2006	49.89
2007	49.99
2008	50.47
2009	50.55
2010	50.69
2011	50.87
2012	51.2
2013	51.86
2014	51.32
2015	52.23
2016	51.86
2017	52.07
2018	51.62
2019	51.33