Year	Percent
1990	17.65
1991	17.64
1992	17.67
1993	17.7
1994	17.72
1995	17.76
1996	17.74
1997	17.72
1998	17.73
1999	17.73
2000	17.73
2001	17.72
2002	17.71
2003	17.73
2004	17.74
2005	17.73
2006	17.92
2007	18.09
2008	18.26
2009	18.42
2010	18.59
2011	18.66
2012	18.72
2013	18.79
2014	18.85
2015	18.92
2016	18.93
2017	18.95
2018	18.96
2019	18.97