Year	Measure
1990	0.648
1991	0.654
1992	0.657
1993	0.661
1994	0.667
1995	0.671
1996	0.671
1997	0.672
1998	0.673
1999	0.676
2000	0.674
2001	0.679
2002	0.683
2003	0.693
2004	0.694
2005	0.695
2006	0.698
2007	0.698
2008	0.703
2009	0.707
2010	0.712
2011	0.717
2012	0.718
2013	0.716
2014	0.718
2015	0.721