Year	Percent
1990	2.6
1991	2.61
1992	2.6
1993	2.55
1994	2.57
1995	2.56
1996	2.56
1997	2.58
1998	2.58
1999	2.55
2000	2.55
2001	2.58
2002	2.6
2003	2.64
2004	2.7
2005	2.73
2006	2.77
2007	2.81
2008	2.83
2009	2.85
2010	2.89
2011	2.93
2012	2.95
2013	2.97
2014	2.97
2015	2.94
2016	2.88
2017	2.9
2018	2.92
2019	2.91