Year	Percent
1990	55.29
1991	55.1
1992	55.2
1993	54.73
1994	54.09
1995	53.31
1996	52.17
1997	51.24
1998	50.61
1999	50.28
2000	51.22
2001	50.82
2002	50.86
2003	51.25
2004	51.7
2005	52.14
2006	52.23
2007	52.13
2008	52.08
2009	51.93
2010	52.88
2011	53.99
2012	55.2
2013	56.21
2014	56.85
2015	57.74
2016	58.14
2017	57.85
2018	57.5
2019	57.95