Year	Measure
1990	0.616
1991	0.611
1992	0.589
1993	0.571
1994	0.549
1995	0.539
1996	0.522
1997	0.526
1998	0.528
1999	0.529
2000	0.535
2001	0.543
2002	0.553
2003	0.563
2004	0.572
2005	0.579
2006	0.586
2007	0.592
2008	0.601
2009	0.603
2010	0.608
2011	0.613
2012	0.617
2013	0.622
2014	0.625
2015	0.627