Year	Measure
1990	0.621
1991	0.629
1992	0.638
1993	0.645
1994	0.652
1995	0.653
1996	0.651
1997	0.647
1998	0.641
1999	0.635
2000	0.629
2001	0.62
2002	0.613
2003	0.611
2004	0.609
2005	0.609
2006	0.612
2007	0.616
2008	0.622
2009	0.63
2010	0.638
2011	0.644
2012	0.652
2013	0.66
2014	0.665
2015	0.666