Year	Percent
1990	15.67
1991	15.63
1992	15.59
1993	15.56
1994	15.55
1995	15.56
1996	15.56
1997	15.56
1998	15.56
1999	15.55
2000	15.54
2001	15.55
2002	15.56
2003	15.57
2004	15.58
2005	15.57
2006	15.59
2007	15.61
2008	15.62
2009	12.96
2010	12.33
2011	12.93
2012	11.02
2013	9.36
2014	10.38
2015	8.78
2016	9.92
2017	10.74
2018	10.68
2019	10.58