Year	Ratio
1973-01-01	0.79063
1974-01-01	0.78516
1975-01-01	0.85386
1976-01-01	0.88962
1977-01-01	0.89476
1978-01-01	0.88906
1979-01-01	0.88078
1980-01-01	0.88099
1981-01-01	0.87637
1982-01-01	0.86960
1983-01-01	0.87082
1984-01-01	0.87517
1985-01-01	0.87798
1986-01-01	0.89798
1987-01-01	0.90643
1988-01-01	0.91329
1989-01-01	0.92157
1990-01-01	0.92775
1991-01-01	0.93894
1992-01-01	0.94740
1993-01-01	0.94801
1994-01-01	0.95439
1995-01-01	0.95826
1996-01-01	0.96358
1997-01-01	0.96993
1998-01-01	0.97150
1999-01-01	0.97725
2000-01-01	0.98188
2001-01-01	0.98729
2002-01-01	0.98563
2003-01-01	0.98693
2004-01-01	0.99099
2005-01-01	0.98912
2006-01-01	0.98676
2007-01-01	0.98364
2008-01-01	0.98508
2009-01-01	0.98432
2010-01-01	0.99287
2011-01-01	0.99510
2012-01-01	0.99213
2013-01-01	0.99436
2014-01-01	0.99386
2015-01-01	0.99157
2016-01-01	0.99164