Year	Percent
1990	50.393
1991	50.756
1992	50.981
1993	51.204
1994	51.428
1995	51.651
1996	51.875
1997	52.098
1998	52.322
1999	52.545
2000	52.769
2001	52.992
2002	53.215
2003	53.437
2004	53.661
2005	53.883
2006	54.105
2007	54.328
2008	54.55
2009	54.772
2010	54.993
2011	55.215
2012	55.356
2013	55.469
2014	55.583
2015	55.696
2016	55.81
2017	55.942