Year	Ratio
1970-01-01	0.375550001859665
1974-01-01	0.454129993915558
1975-01-01	0.413769990205765
1976-01-01	0.410510003566742
1977-01-01	0.411260008811951
1984-01-01	0.570349991321564
1986-01-01	0.579750001430511
1987-01-01	0.553950011730194
1988-01-01	0.565630018711090
1989-01-01	0.592410027980804
1990-01-01	0.644959986209869
1991-01-01	0.661090016365051
1992-01-01	0.659829974174500
1993-01-01	0.676880002021790
1994-01-01	0.684629976749420
1995-01-01	0.678319990634918
1998-01-01	0.704850018024445
2012-01-01	0.751089990139008