Year	Percent
1991	53.09
1992	52.88
1993	51.92
1994	50.84
1995	50.54
1996	50.55
1997	50.65
1998	50.82
1999	48.84
2000	47.09
2001	46.21
2002	44.52
2003	44.33
2004	44.14
2005	45.31
2006	46.7
2007	48.84
2008	50.71
2009	50.74
2010	50.53
2011	50.66
2012	50.68
2013	50.6
2014	51.68
2015	52.37
2016	53.3
2017	54.27
2018	54.82
2019	55.03
2020	54.58