Year	Measure
1990	0.499
1991	0.501
1992	0.486
1993	0.479
1994	0.475
1995	0.465
1996	0.46
1997	0.451
1998	0.442
1999	0.434
2000	0.427
2001	0.427
2002	0.418
2003	0.407
2004	0.406
2005	0.408
2006	0.414
2007	0.421
2008	0.419
2009	0.436
2010	0.452
2011	0.464
2012	0.488
2013	0.498
2014	0.507
2015	0.516