Year	Ratio
1978-01-01	0.854950010776520
1979-01-01	0.859229981899261
1980-01-01	0.861890017986298
1981-01-01	0.862730026245117
1982-01-01	0.872919976711273
1983-01-01	0.883949995040894
1984-01-01	0.886590003967285
1985-01-01	0.871739983558655
1986-01-01	0.888130009174347
1987-01-01	0.939920008182526
1992-01-01	0.956960022449493
1993-01-01	0.953090012073517
1994-01-01	0.953490018844604
1995-01-01	0.953450024127960
1996-01-01	0.953140020370483
1997-01-01	0.956610023975372
1998-01-01	0.980430006980896