Year	Measure
1990	0.615
1991	0.609
1992	0.599
1993	0.586
1994	0.568
1995	0.562
1996	0.567
1997	0.576
1998	0.58
1999	0.586
2000	0.593
2001	0.601
2002	0.602
2003	0.609
2004	0.612
2005	0.613
2006	0.618
2007	0.624
2008	0.629
2009	0.631
2010	0.632
2011	0.638
2012	0.647
2013	0.656
2014	0.662
2015	0.664