Year	Ratio
1971-01-01	0.424430012702942
1972-01-01	0.427379995584488
1973-01-01	0.427969992160797
1974-01-01	0.434650003910065
1975-01-01	0.422760009765625
1976-01-01	0.429899990558624
1977-01-01	0.456239998340607
1978-01-01	0.456149995326996
1979-01-01	0.456739991903305
1980-01-01	0.465990006923676
1981-01-01	0.502560019493103
1982-01-01	0.517030000686646
1983-01-01	0.552690029144287
1984-01-01	0.556010007858276
1985-01-01	0.573459982872009
1986-01-01	0.569360017776489
1987-01-01	0.596319973468781
1988-01-01	0.622179985046387
1989-01-01	0.637090027332306
1993-01-01	0.641969978809357
1996-01-01	0.638859987258911
1999-01-01	0.635370016098022
2000-01-01	0.620320022106171
2001-01-01	0.610509991645813
2003-01-01	0.717840015888214
2004-01-01	0.672980010509491
2007-01-01	0.747470021247864