Year	Percent
1990	49.19
1991	49.04
1992	49.08
1993	49.01
1994	48.96
1995	48.89
1996	48.88
1997	48.85
1998	48.87
1999	49.14
2000	49.27
2001	49.28
2002	49.37
2003	49.45
2004	49.6
2005	49.76
2006	49.99
2007	50.14
2008	50.56
2009	50.99
2010	51.36
2011	51.46
2012	51.72
2013	52.09
2014	52.58
2015	53.14
2016	53.63
2017	54.1
2018	54.48
2019	54.74