Year	Percent
1990	54.51
1991	55.08
1992	55.59
1993	55.97
1994	56.31
1995	56.8
1996	57.17
1997	57.52
1998	57.85
1999	58.17
2000	57.22
2001	56.33
2002	55.48
2003	54.67
2004	53.89
2005	53.14
2006	52.42
2007	51.74
2008	51.09
2009	50.48
2010	49.9
2011	49.22
2012	48.58
2013	47.97
2014	47.4
2015	47.47
2016	47.54
2017	47.63
2018	47.72
2019	47.81