Year	Percent
1990	52.25
1991	52.09
1992	51.95
1993	51.86
1994	51.83
1995	51.89
1996	51.93
1997	52.07
1998	52.3
1999	52.59
2000	52.91
2001	53.17
2002	53.5
2003	53.86
2004	54.24
2005	54.63
2006	54.76
2007	54.9
2008	55.07
2009	55.25
2010	55.43
2011	55.52
2012	55.61
2013	55.69
2014	55.78
2015	55.88
2016	55.93
2017	56.01
2018	56.1
2019	56.21