Year	Ratio
1970-01-01	0.288340002298355
1971-01-01	0.283829987049103
1972-01-01	0.285530000925064
1975-01-01	0.323879987001419
1976-01-01	0.311549991369247
1978-01-01	0.390060007572174
1979-01-01	0.376020014286041
1980-01-01	0.385899990797043
1999-01-01	0.648440003395081
2000-01-01	0.726599991321564
2011-01-01	0.820469975471497
2014-01-01	0.779680013656616
2015-01-01	0.776220023632050