Year	Measure
1990	0.473
1991	0.471
1992	0.468
1993	0.463
1994	0.46
1995	0.459
1996	0.456
1997	0.452
1998	0.45
1999	0.448
2000	0.447
2001	0.451
2002	0.45
2003	0.461
2004	0.474
2005	0.483
2006	0.494
2007	0.506
2008	0.514
2009	0.523
2010	0.53
2011	0.536
2012	0.541
2013	0.546
2014	0.55
2015	0.555