Year	Percent
1990	46.13
1991	50.28
1993	51.15
1995	54.52
1996	55.02
1997	53.82
1998	55.52
1999	53.89
2000	55.31
2001	56.26
2002	52.91
2003	54.06
2004	54.81
2005	58.6
2006	59.01
2007	59.46
2008	60.1
2009	61.36
2010	61.15
2011	61.46
2012	61.65
2013	61.53
2014	60.93
2015	60.92
2016	60.69
2017	60.38