Year	Ratio
1970-01-01	0.389299988746643
1971-01-01	0.411639988422394
1975-01-01	0.356880009174347
1986-01-01	0.638729989528656
1990-01-01	0.616439998149872
1991-01-01	0.589649975299835
1992-01-01	0.615299999713898
1993-01-01	0.603240013122559
1994-01-01	0.643379986286163
1999-01-01	0.746399998664856
2000-01-01	0.779900014400482
2001-01-01	0.806630015373230
2002-01-01	0.802500009536743
2005-01-01	0.826340019702911
2006-01-01	0.821110010147095
2007-01-01	0.821399986743927
2010-01-01	0.864660024642944
2011-01-01	0.914900004863739
2012-01-01	0.948589980602264