Year	Ratio
1971-01-01	0.897279977798462
1972-01-01	0.903199970722198
1973-01-01	0.908420026302338
1974-01-01	0.911140024662018
1975-01-01	0.917919993400574
1976-01-01	0.922450006008148
1977-01-01	0.929719984531403
1978-01-01	0.934490025043488
1981-01-01	0.962019979953766
1991-01-01	0.977190017700195
1992-01-01	0.979380011558533
1993-01-01	0.976849973201752
1998-01-01	0.978730022907257
1999-01-01	0.969389975070953
2000-01-01	0.971189975738525
2001-01-01	0.977020025253296
2002-01-01	0.975820004940033
2004-01-01	0.979849994182587
2005-01-01	0.972150027751923
2006-01-01	0.984420001506805
2007-01-01	0.984690010547638
2008-01-01	0.986379981040955
2009-01-01	0.989740014076233
2010-01-01	0.987890005111694
2011-01-01	0.987160027027130
2012-01-01	0.986010015010834
2013-01-01	0.987139999866486
2014-01-01	1.014709949493410
2015-01-01	0.942189991474152