Year	Measure
1990	0.325
1991	0.331
1992	0.338
1993	0.346
1994	0.347
1995	0.38
1996	0.368
1997	0.388
1998	0.389
1999	0.391
2000	0.387
2001	0.388
2002	0.362
2003	0.366
2004	0.371
2005	0.377
2006	0.387
2007	0.4
2008	0.415
2009	0.43
2010	0.444
2011	0.454
2012	0.459
2013	0.466
2014	0.473
2015	0.476