Year	Measure
1990	0.444
1991	0.442
1992	0.44
1993	0.437
1994	0.435
1995	0.436
1996	0.433
1997	0.434
1998	0.438
1999	0.433
2000	0.437
2001	0.452
2002	0.452
2003	0.455
2004	0.456
2005	0.456
2006	0.456
2007	0.466
2008	0.473
2009	0.48
2010	0.486
2011	0.496
2012	0.501
2013	0.507
2014	0.514
2015	0.518